I voted YABU (just a little) but I need to explain why (and I apologise in advance for it being a wall of waffle).
DH has OCD and it is all about checking doors and household security (which I totally accept makes me biased - but I can see why your DH would be concerned). It's a creeping thing, and it only takes a small incident like this to trigger a new routine. First it's checking the doors, then it's the windows, then it's going outside and checking the back gate/shed/car. And then it's going back and doing it again and again until you're sure. It's like a trickle that becomes a stream and then a river and then a flood.
He would say that he has mild OCD (and I agree ATM) but he has had periods of time over the last decade where it's been worse. Right now, it's pretty stable.
A few weeks ago, I heard a noise outside (long after I'd come to bed) and DH was in the car checking the handbrake, the next day I HAD to ask what he'd been doing because I thought he might be getting worse, turned out he'd moved the car slightly to get the bins past. A total non event that I'd built up in my mind as something else. He was annoyed I'd asked and I felt bad about it.
BUT often if I do challenge a new thing early on, he stops it and it doesn't develop, so although your DH didn't address it in the best way it wasn't necessarily wrong for him to bring it up.
Quoting from your OP:
Anyway since then every night I’ve checked the door is locked before going up to bed, regardless of who was last in even if I know for a fact I’ve locked the door.
The bolded bit is the concern (although we all have moments where we double check things and it's not OCD) and is probably what is making your DH ask.
He didn't go about it the right way (absolutely not!) but it might be a good idea just to clarify between you when you expect the door to be locked and to get reassurance that he won't forget again.