I think Alison essentially covered what I was going to say! But yes, there could be many reasons - a biggie that comes to mind is guilt and awkwardness... as you say it's been 5 years... he perhaps didn't think much of it to begin with but then the time passed by and he didn't know 'how to' bridge the gap that widened as the months and years went by... as such he may be (and I don't know the guy or you... I'm just hazarding a guess on how I would feel in that situation) nervous as hell in how you're going to react... but he has made the step towards trying to reconnect and now the ball so to speak is in your court.

Just a thought

Let us know how things get on which ever route you decide and yes, Welcome to PC!