The following contains spoilers for episode 4 of The Falcon and The Winter Soldier.
The latest episode of The Falcon and The Winter Soldier saw the return of the Dora Milaje, the elite group of warriors that make up Wakanda's special forces. They have come to retrieve Zemo after Bucky broke him out of jail, but instead end up fighting John Walker and Lemar Hoskins, as well as Bucky and Sam when they try to step in. One of the prominent members of the Dora Milaje, Ayo, faces off against Bucky and instantly disarms him... Literally.
At the flip of a switch, apparently, Ayo is able to detach Bucky's metal arm from his body. There is a look of shock on his face after she performs this maneuver, and many fans have taken this to mean that Bucky felt betrayed in that moment. Fans have theorized that he felt hurt that the Wakandans never fully trusted him, as they built this failsafe into his arm in case they ever needed to use it. However, that is a simplified view of the situation and it really wasn't the case that Bucky was betrayed by the Dora Milaje, mostly because he betrayed their trust first.
First of all, logically it makes sense that there would be a fairly easy way for Bucky to take the arm on and off, and the Wakandans would likely be aware of this because it's their tech. If anything, Bucky was perhaps surprised that Ayo knew exactly how to detach the arm, or at the fact that she thought to do it at all. After all, it's a pretty surefire way to quickly end a fight with him. When Sam asks, "Did you know they could do that?" Bucky says no. This is vague, and some have taken this to mean that he didn't know that the arm could be detached. This seems a bit outlandish because it's literally a part of his body and at this point, he's probably familiar with how it can be removed. Again, he was probably just surprised that Ayo specifically, or that anyone other than himself or Shuri (who presumably built the arm in the first place) knew how to detach it.
Some fans have pointed out that this move would be upsetting for Bucky because he's a person who has had his bodily autonomy taken from him for years as the Winter Soldier, and now that he finally has that back, Ayo violated that freedom by literally (albeit very briefly) robbing him of a limb. This is a fair point, but she was only trying to end the fight, not disable him for good. She would have been within her rights to take the arm away, as it's vibranium and therefore technically belongs to Wakanda, but she didn't want to be that extreme. If anything, it was as if she was letting him off with a warning. It's reminiscent of the "I brought you into this world, so I can take you out of it" phrase that mothers often use with their children - Ayo is reminding him that Wakanda gave him his mental freedom as well as that arm, and if he continues to be an obstacle, they could just as easily take it away.
That's the most important thing to note in the situation - this hostility didn't just come out of nowhere. Bucky broke Zemo out of jail, knowing full well that the Wakandans would come after him. After all, this is the man that killed their king, as well as countless other innocent people. After everything that Wakanda did for Bucky (which we partially see at the beginning of the episode with the flashback scene between Ayo and Bucky in Wakanda), they would obviously view it as a slight against them that he would break this criminal out of jail simply as a means to his own ends. Ayo and Bucky also clearly bonded during his time in Wakanda, as we see in the scene where he breaks free of the Winter Soldier programming for good. Perhaps Ayo feels particularly upset with him as a friend and confidant; she notably calls him "James" instead of "White Wolf", which displays an odd formality and perhaps lack of trust.
Again, the Wakandans don't owe him anything. They took care of him out of the goodness of their own hearts, literally putting their people in danger by harboring a fugitive who was still trying to overcome assassin brainwashing. They gave him sanctuary and peace, as well as a brand new arm made of Wakandan technology, and asked for nothing in return. It makes sense that they would be upset that he would betray them by breaking Zemo out of jail and allying with him. He was using their gift to him (the arm) as a weapon against them, and so Ayo quickly shut it down and reminded him that the only reason he's in the position he is (and the only reason he has that arm in the first place) is because of Wakanda. Deactivating the arm was simply a failsafe to ensure that the Wakandans couldn't have their own tech used against them in a violent way.
So was detaching Bucky's arm a "betrayal" of his trust? Not really. He was the one who has betrayed trust in the first place, and taking the arm out of commission briefly is a pretty gentle reminder from Ayo about where Bucky's allegiances should lie. In general, this connection between Bucky and the Wakandans who helped him is a really interesting dynamic, and hopefully it gets further explored in the next couple episodes of the series.