Yes, review bombing does happen for various reasons. A game can get a lot of negative user scores for reasons that have absolutely nothing to do with the quality of the game, often political. Or tribal, with users being upset that a game is either exclusive to a certain platform, or not exclusive. Cyberpunk 2077 is being review bombed (presumably by Russians) after the Polish CD Projekt Red pulled the game from sales in Russia and Belarus over the invasion of neighboring Ukraine. There are some borderline cases, like a game getting bad user scores for issues like monetization. But in general I would define review bombing as not actually being about the game being good or bad.

Tunic and Elden Ring having lower user scores than critic scores is a very different phenomenon. Elden Ring is so successful, I recently even saw a TV ad for it on a major French TV channel during prime time. And nowhere in the ads does it inform you that if you are not very good at action games, you won't have much fun. Tunic is, if anything, even more deceptive, because it looks so cute. It looks like a game for children, but it is likely to make first the child and then daddy cry. As one of my commenters remarked, if you buy a book or a movie that is too challenging for you, at least you can read or watch it to the end if you so desire. Brutally hard video games simply stop you from getting past certain points if they are too challenging for you. If you buy Tunic or Elden Ring, play it for a few hours and then rage quit, you are completely justified to rate the game low on Metacritic or Steam. Yes, it is a problem of the game "not being for you", but in absence of a warning label that is the game's fault. The infinite health cheat mode that I used to play Elden Ring should be included in the game as a "story mode difficulty".