Google doesn't use chrony specifically, just an algorithm that is somewhat chrony-like (but very different in other ways). It's called Google TrueTime.
Ah yeah. For VPS tenants it makes sense they would default to Chrony. They have a public facing pool of NTP servers at `time.google.com`, and for tenant use they provide `metadata.google.internal`, which is probably where the Chrony config file points. IIRC TrueTime is not actually open source and is only used internally on their infrastructure.