Because the only downvoating I did this week was in a flame war with GA mods. I’ve been largely inactive other than that.

To be fair, that may have been enough to catch the algorithm. However, those I was arguing with got a builder post.

Were you downvoating everything they said? Were they downvoating everything you said? i.e. Same behavior but different outcome? Were they warned?

Drawing conclusions on spotty information is never a great idea. I would like a clear definition of "vote brigading". I think a lot of people would. It ought to be in the user agreement.