£1000 more than quoted

I’m torn between two thought processes here and wondered if I’m being stupid.

I’ve just had a composite decking done in my garden, totalling £2112.
I’m very pleased with it, no issues with the work whatsoever etc.

They left this afternoon, then the owner of the company returned 45 minutes later, apologising looking sheepish and embarrassed.

He said it was completely his fault, but that he’d done the maths wrong and his quote was £1000 less than it should have been. Again, he was said himself he was embarrassed and that we absolutely did not have to pay anything more if we didn’t want to, but he thought he’d point it out.

Am I being absolutely played? (I suspect I am). Or is there a chance this is a completely honest mistake?

I would potentially give him some extra, but not another grand, I’m just wondering if this is all a ridiculous way of completely hooking people.

(I’ve had a thorough look online again and it’s a family business, all excellent reviews so I’m really not sure).