Danny Batth’s header from Jordan Graham’s corner just 61 seconds into the contest was enough for a 1-0 victory for the hosts.
It meant the Lilywhites ended the season in an identical position to 12 months ago, on 62 points in 11th, having lost five of their last six games.
"It was a poor goal to give away,” said Grayson.
"The last thing we said before we went out was to make sure we were nice and solid and gave ourselves a base to play from.
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"We have been a bit too easy to play against in the last few weeks, given too many goals away.
"So for their main player to get a header as easily as he did was hugely disappointing.
"There were parts of the game where we did alright and parts when we didn't get the shape back in place to deal with the threats Wolves had.
"It is always difficult when you give the home side an advantage of an early goal, that lifted their supporters.
"That probably epitomised the last two or three weeks when we have not been at our best in many departments."