I don't know but if it can run on one, it can be created on one. And while I'm not 100% sure, given the custom hardware in the C64 and the fact that Pitfall was released in 1984, I doubt there would have been anything better to develop on and I don't think cross-compilers for the C64 came along until later.

I believe it was pretty common to develop C64 games on the C64 though I would imagine it was also common to use RAM expansions and hard drives to make development easier, faster and more convenient.