So I tried talking to the shy guy at my college I liked and turns out he wasn't exactly shy

I talked about having a crush on this guy at my college who is shy and doesn't talk to anyone and mainly sits in a corner and reads Harry Potter. I thought he didn't talk to anyone because he was shy. Turns out that wasn't the case. I went to try to talk to him and he pulled out a piece of paper and pointed at it. I didn't understand what he was trying to say at first, but then I got he wanted a pen. I didn't have one and he started using sign language. I said "Oh! You're deaf!" He shook his head no. I know the sign language alphabet so I asked him to spell it. He sign spelled the word MUTE. I said "OOOOH!" So I went to find a pen and we went to the cafe together and that's how we communicated. I made sure to not talk too much so he could write his response. We actually had a good conversation and be made me really want yo take sign language again next semester because he's really cool and I really like him. I ended up chickening out on asking him on am actual date though.

Also could someone explain being mute to me a little.

I meant more why is someone mute. Is it a physical thing or do they choose not to speak.