I don't see how this warrants a warning, you literally pushed yourself a few cm's and it didn't affect anyone else, you were clearly not out to cause trouble.
If you follow the staff ethos:
We don’t want people that break very minor rules that have no impact on other people being needlessly punished when a simple talk can resolve the situation.
This punishment looks pretty stupid, especially without a verbal.
Of course, I don't know the whole story or if there's anything else that was not included in your recording, i'm just giving my opinion on what has been provided so far.