Hiya, Max has had these twice before, both times they've appeared for no apparent reason, have not caused him any bother at all, and have faded over a matter of weeks and disappeared.
The first time Max had an antibiotic jab and some eye drops, but I think that was more of a precaution as he has FIV, but the follow-up visits didn't show anything, and we never found out what caused it to be honest. We think it was a burst blood vessel.
A bit of a mystery
If you're worried it might be worth following up with your own vet as well?