If I was her, I would be thanking my lucky stars I found out about his "weirdness" on the first date, instead of later, say, at the rehearsal dinner.
Unless she is very forgiving or really needs someone to date, I would NOT be going on another date with this guy.
I go with this.
You can come up with a convoluted explanation that is relatively benign - he's got a phobia about sitting next to someone eating popcorn, but is embarrassed about it, so he was trying to eat all the popcorn before she got back, but didn't manage it, so he had to resort to making it as hard as possible to eat it, and is now ignoring it, and planning never to go to the movies with her again so he doesn't have to explain this.
Or, you can go with a much simpler, and much more likely explanation - he's got food issues of some sort, or it's a move, conscious or unconscious, to test whether she'll put up with bad treatment without standing up for herself, if she's kept off balance.
If she *is* still dating
him, and she can't say "By the way, what was going on with the popcorn thing on our first date?" and get a decent answer, she's not headed for a particularly healthy or good relationship