Agree it does look like blood pooled under the mucosa. In normal "detumescence", you'd expect it to go back to normal within minutes to maybe hours, and you wouldn't expect the bumps to deform the surface of the penis significantly. The fairly large raised texture and the fact they're described as being hard makes it look abnormal to me, more like hematomas, but it's hard to tell from video.
If it disappears quickly and occurs every time you play, it might be normal, but I think a likely causes to consider on an otherwise healthy dog would be excess pressure in the blood vessels by something like "milking" from base to tip or excessive suction. Based on story, I'm gonna guess it's a hickey. Either way, should get better if you leave it alone a few days. Maybe review how you're handling that thing in the future if that's what's going on.