How do you know this friend wasn't actually interested in her at first, but changed his mind and is now trying to let her down gently. It happens ALL THE TIME and nobody is obligated to call someone and hang out again just because they asked for a phone number or spent a night talking to them. No contract was signed.

It's clear my opinion is in the minority here, but The dating world is not always fair and you need to have a tough skin. People don't have to do the thing you want just because you perceived them to feel a certain way. When it doesn't work out, you act like an adult about it and move on to someone who does want to spend time with you.

It's cool to have a different opinion and there's no sense in me continuing this argument, but I don't think the guy is scum because he talked to OP for a night, asked for her number and decided not to persue the relationship.