Ah, I was wrong, the docs state what’s happening here:
https://restic.readthedocs.io/en/latest/100_references.html#locks
The field exclusive defines the type of lock. When a new lock is to be created, restic checks all locks in the repository. When a lock is found, it is tested if the lock is stale, which is the case for locks with timestamps older than 30 minutes. If the lock was created on the same machine, even for younger locks it is tested whether the process is still alive by sending a signal to it. If that fails, restic assumes that the process is dead and considers the lock to be stale.