In my opinion, the question comes down to "what is a valid criticism". I think the bombing part, where a lot of people give a similar negative review at the same time is secondary.

If a game releases in a borderline unplayable state this warrants negative reviews. It shouldn't matter how many of them there are and if they are all in a similar time frame. Same with an update that harms the game a lot. If this makes the game change the rating from positive to mixed or negative, I think that's fair because if I buy the game now, I will get it in the most recent state and if this is shit I don't care if it was better at some point in the past, I'm glad if I get a warning through the reviews.

If the game gets negative reviews because a person/group related to creating the game said or did something that a large group of people disagree with it's more complicated. It boils down to if you can/want to separate the art from the artist and if you find that criticized thing bad in the first place. If you don't think this is a valid criticism you probably think this "review bombing" is a bad thing.

I think the term "review bombing" is used to imply that the criticism has nothing to do with the game itself. But like with all terms, the usage becomes broader and broader until it changes or loses meaning completely.

Since Steam reviews contain written explanations it is easy to check why the game gets the negative attention. I never came across a game that had a lot of reviews for an unrelated thing where almost all the negative reviews lied and said it was bad for gameplay reasons.