Playstation was in development and was released in japan almost a year before 3dfx released their first card. It's reasonable to draw that someone could have had experience working on the playstation graphics system prior to moving over and creating 3dfx. The fact they were building a prototype system for Sega as well means they were likely involved in that space before. SGI also licensed the CPU to sony for the playstation and back then the CPU would have done most of the graphics workload for the playstation - similar to an APU today with even less segregation between gpu and cpu.

https://archive.computerhistory.org/resources/access/text/20...

very good background on the founders up to and at the creation of 3dfx... some really interesting stuff in there.