It's not the case.

You should think of Piper as a single filesystem which permits atomic multi-file edits. And that's about it; there's nothing in that which forces any particular release structure on you.

The talk did mention (briefly) that monolithic codebase and monolithic binaries/software aren't strictly related. It's likely that monolithic software is easier in a monolithic codebase, but I don't think that microservices are harder in a monolithic codebase. Yes, we tend to statically link, but that's for library dependencies (i.e. things like the protocol buffers libraries/definitions). I don't work at all in this area, so this is a guess, but I imagine that it's extremely rare for unrelated teams to have application logic linked into the same binary - just making a release would involve coordination from so many teams :)