Yes, it is. You are probably confusing Piper, the internal name for the VCS, with Google Piper [1], which is a completely separate and unrelated project. That project seems a closer match to Monomake.
This was a common problem with Google, actually. There would be an internal name but once released it would take on a different name. Sometimes that name would conflict with a different internal name, which then made internal searches impossible. I forget the specifics, but Buzz became an external product but was an internal product name for something different.
Dart (the language) was internally known as Dash prior to release. IIRC Google Dash was an external thing for advertisers or something like that.
So when I say Piper I really do mean the internal rewrite of Perforce.
Buck2 is much faster than Buck and pretty great for the set of problems it's trying to solve. (I'm skeptical that the corner that Meta has painted itself into is good, but assuming that that can't change, buck2 is great.)
Remote builds are common now, from what I've heard.
Sapling is the name for Meta's fork of Mercurial. Piper is not a reimplementation of Perforce, by the way. The closest equivalent that Meta has to Piper is their source control server Mononoke.