The English translation given is ‘I haven’t got a clue as to why he quit so suddenly’. Can wyszedł also mean ‘quit’ as well as ‘left’?
In this context, “wyszedł” can only mean “left (a room / a building)”. So it can mean “quit” when “quit” is understood literally, but not when it’s used to mean “resigned from a job” or “stopped an activity”.
I think “why he left so suddenly” would be a better translation here since it’s more natural and less ambiguous at the same time.
Thanks, I’ll report it next time I see it.