Yes, the server is based on Perforce, called Piper, but the CLI is based on mercurial. So locally you're doing hg and then when you create a CL, it translates it into what p4 needs.

> Google bought a license for source code and customised it.

That makes sense because vanilla Perforce is unbearably slow and impossible to scale.

Last I checked, it was bought by Private Equity firms and actual product development had more or less stopped.