Mark,
Gam Gong Kyun is part of Lai Ng Sam's lineage. It is not a Hung Kyun form and unique to our lineage as far as I know. It is not "Shaolin" in origin as far as I know.
Gam Gong Kyun, as I learned it, is from Guang Xi or Yunnan regions (near the Thai/Laos border) and was picked up by Sizou Lai during his travels. You are correct in saying it looks like it could be Thai Boxing. There are certain parts that look at bit Wai Kru'ish and the form places a big emphasis on the use of elbows, knees, etc. If you're doing research then I would encourage you to take a look at some traditional Muay Boran, Muai Thai Chaiya, etc. That may give you some insights.
Hope that helps. Private message me if you have any other questions.
Justin