OTOH, it was a federal court. His lawyers could just take this up the ladder.
In the end, it comes down to does the right to free expression include the right to be heard? After all, Trump blocking them doesn't stop them from tweeting whatever the hell they want about him. It just means he won't see any of it.
EDIT: Ah, hadn't realized that Twitter's block function also stops the blocked person from seeing the blocker's tweets, unlike our Ignore which is only one way. Now this makes more sense. Yes, participating in a public forum does require one to be able to read what is being discussed and blocking could arguably interfere with that.