That means he or she is emotionally uncomfortable about something and doesn't care enough or hasn't thought about yours. Or he or she simply doesn't care and left you to the sidelines, which, in the first place you are only a hookup anyways. Update us in a week or a month......

You can't get ghosted by someone who lives next door. You'll be able to physically see him often. The term you're looking for is "unceremoniously dumped."

My advice- go get tested for STI’s and then move on. My gut feeling (or random guess) is that he or she was likely not exclusive, as you have no comment about that, and there may be some awkwardness somewhere in the relationship, like becoming exclusive/involved with someone else, or a positive test on you neighbors part (pregnancy, STI, COVID, whatever) they don’t want to talk to you about. Alternatively it’s just that this person is not interested any more, and doesn’t know how to end a relationship that was never really defined or officially started in the first place. I mean how do you dump someone you’re not dating? Either way - advice is the same: get a STI test and get over it.

How do you know you've been ghosted if it's only been one DAY? Someone not talking to you for one day doesn't necessarily mean anything, much less they don't want to see you ever again...