It's worded confusingly. Let me see if I'm correct here:

If people prevent something being used by tons of other people for no good reason

This is not in reference to the lemmy.world users being prevented from using the instance, but instead is about the possible motivation of said attack

then this would be a very good one to “hold a grudge” against them for.

Continuing on to say that you could understand how a person could hold a grudge over a perceived slight

The way you worded it make it sound like you mean lemmy.world users should hold a grudge against the attackers for preventing them from using lemmy.world, which is why people are confused. It might have been better to say like "The attackers are probably retaliating for being banned or something"