It used to be the norm to write games in C. In fact it used to be the norm to write them in assembly, C was seen as a higher level abstraction that sped up games development once upon a time.
Yeah, I'm pretty sure most game devs of that era were doing something similar. It seems that once games went 3D, it was too impractical to do assembly anymore. So basically a lot of early PS1/N64/Saturn games were likely some pretty rough C code if I had to guess.
It's less that but that the C tooling matured to the point where it was actually good enough to use. Particularly in terms of good enough output. Tight loops and often called functions were and sometimes still are (in SIMD terms) written in assembly so they could be hand optimized.
More exotic hardware also relied on the vendors providing a C compiler and the quality there could vary wildly.
