All he said was that Schooly D influenced him. Everybody knows that 6 In The Morning was influenced by PSK, but that doesn't make PSK a "gangsta rap record".
If PSK is "gangsta rap" as you say it is, quote some lyrics from PSK to support your premise.
My premise is that rappers started cursing in the mid 80s, but when Colors dropped, along with the movie, it was like something completely new. Colors had a music video and the effect was so devestating that gangs started popping up in Boston where there were no gangs prior to Colors.
We had no idea that there were gangs in LA called Bloods and Crips that wore red and blue. Nobody knew that until Colors came outaround the spring of 1988. Ice T's second album came out at the end of the summer (although Colors wasn't on his album, it was on the Colors Soundtrack) Eazy E and NWA's albums came out after Ice T's second album.
By the time Ice T and lster NWA came out, Schooly D was more of an afterthought. He didn't make any music videos until much later and didnt have anywhere near the impact of Ice T or NWA.
Anyway, I'm still waiting for you to post some songs or lyrics that would be considered "gangsta rap" that came out before Colors.