He may not connect "RI" to "respitory infection". At any rate, instead of cutting the guy off and gloating about a superior level of knowledge, you could instead have explained 'respitory infection' and given some symptoms, or even pointed him to a website(lik this one) where he could learn.

I know vets that don't realize initial terms for illnesses. It happens and everyone was new once. The length of time you've owned something doesn't mean you know what you're doing. After all, we've all heard of ball pythons being kept in a tank with no heat for years and still alive. Does that mean that it's right? No, it means they've been doing it wrong for a long time. You can own animals for decades and be a noob to proper care.

Only education can fix it.