Big oof, that’s most likely what happened. If someone goes alone there’s not much they can do if they end up having to go after they already bought their drink and snacks. When I worked at a theatre some people would leave their snacks with me temporarily when I worked at the booth where we accepted tickets to let people in, so for anyone who likes to go to movies solo, that’s usually a good option. That or you can find someone seated nearby in the theatre and ask them to let people know that the snacks you’re leaving at your seat are claimed and not abandoned. Or bring a note to put with your snacks as a last ditch effort.