Assuming bad faith without evidence is a big part of the issue here.
You specifically asked "What's the ulterior motive here?" which implies you think there is an ulterior motive. An ulterior motive would be acting in bad faith, since it would by definition be different than the expressed motive, since the reasoning was clearly expressed above.
Presentation matters. Whether you meant it to be or not, your statement is somewhat inflammatory, for the reasons I just outlined. In my opinion, it's also a very good reason why the temporary ban is a good idea.
I was very specific to outline an additional condition which I think makes all the difference, which is that you were presented with the reason for the action. Assuming an ulterior motive when you've already been given an explicit motive is assuming they are acting in bad faith, and that that they've provided a reason that does not match reality.