When else would they post a negative review? The negative change just happened, so it makes sense that players would be posting negative reviews now.
As for why people are responding negatively to this being called review bombing, a lot times the term is used to dismiss the bad reviews. “Those aren’t real negative reviews, we just got review bombed. Those players sure are fickle, aren’t they?” Basically calling it review bombing just makes it sound like the negative reviews aren’t legitimate and don’t have a valid reason to recommend against the game.