Interesting that he wants to know what you intend to use the computer for or he won't respond. If he's getting rid of it what does it matter what you're going to do with it?
Maybe he just wants to be sure it goes to a good home, and not to be re-sold? Seems like a good way to make sure that it goes to someone who really wants it for what it is. Or at least says the right thing.
I got my ][+ from a similar listing.
While my guy wasn't as blunt, I knew he'd have tons of replies.
So I told him about how it was my first computer, having to save up for it, etc.
He said he gave it to me because my story was similar to his own.