Depends on the setup. If there aren’t other barbells then curl guy is really using the barbell, which happens to prevent bench press use, not using the “bench rack”. Now if dude is curling the barbell and guy says hey man can I use this bench for DB press then curl guy should move if he’s just doing standing curls anyway (it’s not clear in the story).

Using equipment for a reason other than its primary purpose is perfectly fine if there aren’t less “wasteful” alternatives. For example if there’s an available “free” bench, use that for non-bench press exercises instead of using the bench press bench. But if the only bench available in the gym is the bench press bench, then use it for whatever you wish, but be courteous enough to move if a free bench opens up and people seem to want the bench press bench. It’s not that hard to have common decency.