My son caught this in his pond yesterday. The pond was completely renovated in 2012 so there is no chance of any carryover from previous administrations.
The only sunfish species we stocked were some HBG which I bought from a local fish hatchery and some RES from Shorty and/or TJ.
Is it a pumpkinseed or did my HBG manage to pull off a spawn and hatch something trending toward a GSF?

Pretty fish, love the colors. Looks like a HBG with heavy GSF traits in my opinion, the mouth just doesn't look large enough to be pure GSF. Your HBG could have pulled off a spawn and seen some recruitment, I wouldn't be surprised if they had. While HBG are mostly male, a few females in the bunch and they are quite capable of producing YOY.

Not a P-seed, but a very colorful HBG in my opinion.

Ditto

If HBG and RES were the only fish in the pond, the only possibilities would be:

HBG male X HBG female
HBG male X RES female
RES male X HBG female

From what I have read, GSF female X RES male is easily accomplished in the wild. While GSF male X RES female is not (although can be done easily artificially). I don't know if this would carry over that HBG male X RES female would be unlikely also or not.

Another possibility, is this is an F1 fish. One of the original stockers.