Were the other defenders aware that this was your plan? If they weren't, that is grounds for a ban. Plus they need to support it. I know a lot of people will say that opening gates/doors/etc is grounds for a ban but when a majority of the defenders is aware of it and are ok with it, then I don't think it's a big deal even if it backfires since it was a strategy planned by the defense.
Is that what occurred? Or were you just doing this on your own, thinking it'd help? It kind of sounds like you went on your own and decided to do this which would justify a ban imo.
And like uther said, it's temporary so don't worry too much. They let you know if its a perma. (which ironically never really is a perma in this mod)