I don't think you're uptight, teenagers are well umm err teenager.
I'm coming cold to this, but I recall being a 17 year old bloke.
Not all is lost as far as I can tell. He did ring you, frankly at 17 I wouldn't have.
As for him being in a ditch, recalling some of my 17 yo drunken journeys home, he's probably safer at the other house, unless you go and pick him up.
Also, my parents didn't know the names of my friends. So I wouldn't sweat that, I think very few parents do at that age. Indeed I would worry about a 17 yo who had that few friends.
He may get some grief from the other parents, but that's part of growing up. The girl's issues with her parents are not your problem. Also he may have good reasons to want to stay at her house...
Also it was a Friday night, not a school night, so that's less bad, in my opinion.
As for failing at school, like you I see that as a related problem, but one with different things you can do about it.
I think it's important to pick battles you can win, and as he gets older that number drops. If you fight in circumstances where he can "win" merely by ignoring you on the phone, then he will be more difficult to control in other circumstances.
I'm sort of with DP in that at 17 there's no obvious way you can force him to obey you, certainly not at a distance.
I can see some opportunities in terms of sticks and carrots. He clearly wants more of a social life, perhaps youcan trade improved school performance for help on that front.
Maybe a party at your house if he achieves better results ?