Daniel is a human. A strange human, but a human non-the-less. And no he didn't get sucked into Equestria through his computer screen.
Daniel was born and raised in Equestria to a pony mother and father, treated as an abnormality in genetics by most. Quite a bizarre abnormality, mind.
He went about his business undisturbed by most, but there are six ponies in particular that want one thing from him. Hot, sloppy, unadulterated, passionate sex.