Guy I like replied to me on Facebook but…. it's so emotionless?

[Christopher]

Im a girl using my brother's account.
I like this guy in my medical school and I'm the only girl he sits with in lectures otherwise he sits alone. I sometimes catch him glance at me..
He lacks friends because he is SO introverted!!! He does everything alone, doesn't engage in conversation and is very very quiet.
He never goes on Facebook either because he never 'sees' all the messages regarding medical projects and assignments.
Anyway, he wasn't in school on friday so I sent him a message ''hey you weren't in today were you, everything okay? '' and he actually replied!!!! He replied the morning after, so it was very soon. BUT his response was a very emotionless and dull: ''
Yeah, I was just feeling ill but I should be better by Monday''

Why does he show subtle signs of interest and reply so dull-y? He didnt even say thanks for asking or put a mere smiley face… When I see him tomorrow how should I react? Should I ignore him? Or should I sit next to him in the lecture like i normally would?

[a person :P]

Relax. It's no big deal. It's not like your close

[Jan409]

He lacks social skills, so off course he isn't going to add smileys, or say thanks for asking
Just don't get over excited about him, as he may already have a g/f
and he doesn't seem much of a catch anyway

UK