This is not common practice. Google has had a strict no iCloud, no Dropbox policy for a while. We can't even have code from the core codebase stored locally on our company issued laptops.
SWEs are issued a desktop machine, and a laptop. The laptop (Mac, Linux or Windows; employee's choice) is essentially a very expensive remote desktop client. All development work (except some OSS stuff) is performed on the desktop machine.
(Or that's how it was when I worked there until 2016.)
Yes chromebooks are very common developer laptops, up there in numbers with (still most popular) macbooks and linux laptops. They are more than sufficient for the lion's share of engineering roles. Corp engineering is pushing them hard because they are cheap and secure.
Roughly that, although it uses a Google-developed internal tool. Source code files can be transferred to one's workstation (which lives in a Google building), but not to one's laptop—all work on a laptop must be done through a remote session, either SSH, VNC, or via a (again Google-internal/proprietary) cloud-based editor.
But even those aren't allowed to be mounted to your corp laptop. Those clients can only be mounted on a workstation unless you are doing iOS development.
Does that make it feel more like he was intentionally storing company files in a personal account?