There’s a bit more to it than captured in the summary, which is why it’s just a summary of the spec and not the actual spec.
From a bit further down on that page:
- Major version zero (0.y.z) is for initial development. Anything MAY change at any time. The public API SHOULD NOT be considered stable.
Lemmy is still in major version zero, so it can make breaking changes without incrementing the major version and still be in compliance with the spec. This way, projects won’t have their first “real” version be something like v123.0.0.
Lemmy still being v0.x also serves as kind of a warning to app developers that changes like this may be made at any time.
If they have the root access typically needed to reboot a server1 they could also just wipe the logs without rebooting.
1: GUIs typically have a way to reboot without such privileges, but those are typically not installed on machines just used as servers.