Violate the agency of one player as DM is different from a NPC violating the characters agency
As a player, your role is to play your character. You know the spirit of your characters, their feelings and their priorities better than anyone else. And all this knowledge goes together to enable you to play the role assigned to you in the rules (PHB, 6):
The players describe what they want to do …
Of course, what your character remembers and can not remember is an important part of that decision. It is therefore unambiguous that the agency is violated here. But it's important to realize that there is a difference between a DM violating your agency as a player and a NPC violating your character's agency.
NPCs can violate characters agency
If a lich drops a character at 0 CV with a magic missile spell, characters the agency was raped. They can want to get up and attack the lich, but they can not because their body is too damaged to allow it. Similarly, if a vampire uses his abilities to charm a character, the agency of this character has been violated. The character would normally want to attack the vampire, but he can not because he is Charm.
These types of violations are may not be very fun for the player. This means that you do not have much choice in this area, or at least that your choices are severely restricted. If this is done often enough, these violations can eliminate all the fun of the game, which is often meant to be a fantasy of empowerment. But they do not constitute a violation of the agreement between the player and the DM to control the elements of the game that are assigned to them.
Playing with your character's memories is an established element of the rules that your DM can impose on your character through forces in your environment. In the same way, your characters can be knocked out at 0 CV by damage or Charmthey can be under the influence of the 5th level spell Edit memory. And the creature that cast this spell could be so powerful that the CD on the spell was too high for a roll of dice to be overcome (for example, DC 70). While this may be a frustrating result (and the DM should not use it often, unless the game is more fun for the players), it's something that could happen in the story, and does not necessarily constitute a violation of your agency. player.
But this could also be a violation of your agency as a player by a DM, depending on how the deal has unfolded
A violation of your agency as a player occurs when your DM decides what your player wants to do for you as a DM. Although the DM may subject your character to a number of external influences (magic spells or ugly Presence of an Ancient Dragon) that could restrict what your character can do, he can not take it away. control without resorting to any of these external forces. If you say "I get up and keep away", the SM can not say "No, it would be boring, you sit and listen." It would basically be that the player is useless at the table: the DM controls everything, including you, and you're right there to roll dice.
Removing the memory of your character does not necessarily constitute a violation of your agency as a player: it seems that the terms of the agreement have been discussed, this outdoor aircraft constituting a group. So, it would be a violation of your agency as a player to decree that your player has agreed to name you, the player, never heard of.
If the "PC in question" had the opportunity to chat privately with the outside aircraft (as the player had discussed with the DM), the transaction might have been changed without your knowledge. It would be frustrating, but not necessarily a violation of your agency. But if the agreement has to be discussed in public, you should have the opportunity, as a player, to describe your player's reaction. Otherwise, your agency as a player has been violated.