Sounds like a database migration [by Google that is] or dump/reimport that hasn't preserved the original primary/foreign keys and so items are now owned by other people. Oh the joys of referential integrity.
The ownership of things seems to have been kept within your company but not so for individual items in the calendar which could mean that random other people are seeing your calendar entries appearing in their calendars.
The ownership of things seems to have been kept within your company but not so for individual items in the calendar which could mean that random other people are seeing your calendar entries appearing in their calendars.
"Oops" is the operative word from Google.