What OS was it running? or did he compile Cpython from source?

CM5 used solaris front ends, back ends didn't have an OS.

This is the talk: https://m.youtube.com/watch?v=4RSht_aV7AU, it is a full hour. Quite enjoyable but light on in depth technical stuff. Don't recall hem mentioning how git python running technically, it is more about how he came in the position to do so in the first place.