Under what circumstances will a girl give her mobile phone number to a strange boy?

What impressed me most was getting on my neighbor's bus from home to school. He said he couldn't find his cell phone and borrowed mine. Then he got my phone number (I was only 18, so don't laugh at me for being stupid), and then he often texted me and called me boyfriend! In the end, I can't remember how I successfully refused him. The feeling at that time is where you gain confidence. I am an undergraduate in a key university, and you are a junior college student in a vocational and technical college (I think you must find someone smarter than yourself when looking for a boyfriend, who can be neither tall nor handsome, who can be poor at home, but whose school education is worse than mine), but I feel looked down upon.