I mean isn't the definition of prejudice having preconceived notions? If someone has never dated a shorter person and is automatically barring the possibility of dating them, that's prejudice. If they have dated someone under a certain height and didn't like it for whatever reason, then that's a preference. I think not finding someone attractive on the basis of height alone is pretty shallow at least. Like if someone is otherwise extremely attractive, in shape, good personality, you're really going to pass because some arbitrary height restriction?
Sure it's shallow, but I don't agree that it's necessarily a preconceived notion.
Saying something like "I don't date fat people people they're lazy" is a preconceived notion (not all fat people are lazy, and I've seen some fat people that are more agile than I will ever be). I assume something similar for short people would be "I don't like short people because they're not strong to lift me up" or something. To be honest I can't even think of an example that makes sense.
"I don't like short people" is as shallow as "I don't like fat people". But it's not a preconceived notion, nor is it prejudice. It's a "shallow" preference for a specific physical trait. And again, I agree its "shallow" if we're talking about people evaluating potential partners based on physical instead of personality traits, but I'm not going to call it prejudice and I wouldn't even dream of comparing it to racism.
I have physical preferences for what I consider attractive, like, right when I meet someone I can either be physically attracted to that person based on their looks, but if I have to time to get to meet that person I can be turned off due to personality traits. The opposite is true as well: I may not find someone physically attractive right away due to certain traits, but I can sure as hell find them attractive after hanging out for a while and getting to know them.
Neither men nor women have the obligation to sit down and have a conversation with someone they consider physically unattractive, just to give them a chance to become attracted to them on the basis of their personality. It's cool if it happens, but it's on them to make that choice. Online dating is mostly about looks unless you can show in your profile that you're someone that's worth at least meeting once. If you're chatting with someone and they ask for a specific physical trait to "filter" by, then perhaps that person isn't worth your time?