I have hooked some good size grass pickerel on Little Grassy over the years, but never got one on Kinkaid. I would tend to say yes grass pickerel are in the creeks flowing into Kinkaid which means they could be in the shallows on Kinkaid. I have caught log perch and other small stream fish by Sharp Rock, Levan, and other small creeks, so you just never know what that pic really is. Pretty clear pic for Kinkaid, but if that is what you say I believe you. Natural reporduction is not out of the question for Lake Kinkaid since we have a natural muskie strain going through the motions every Spring. If we had a slow warm up lasting over several weeks instead of a peak in high temps very quickly, we might see the RARE occasion of a fingerling making it to the size in you picture.

These are just my opinions
Scott