I think it just means that he's the only cat who's presented with those symptoms lately Vet nurses are psychic

When I rang to get Mini and Jasmine boarded at the vet's for a couple of days, she said "and how about their booster shots while they're here?" She didn't even have our file open!

Good luck with Basil. Sounds like an allergy from your symptons but I'm not a vet, so all I can do is wish him the best