Putting myself in your shoes, I would have helped him by telling him I notified his nurse and she'd be in shortly. In a few minutes, I'd check on the patient and remind the nurse again. If I was really concerned, I'd let the nurse know if she doesn't have time to assess the patient I'd be happy to get someone else to look at him. You can bet your bottom dollar though, I'd call 911 before I gave him a breathing treatment!
You not only do not have a duty to administer breathing treatments to patients no matter how much you believe they need them, you don't have the authority to do so either. How do you even know the patient was allowed a breathing treatment? What if they had been discontinued? Or if he'd just had one earlier and it wasn't time for one? You not only don't have the skills to determine if the patient needed a breathing treatment, you don't have the information necessary before providing one. I'm a nurse but I can't give a breathing treatment because I think a patient needs it, I have to have an order for it. If the order is for a treatment every 8 hours, I can't give one every 4 just because I think he needs it, I have to call and get an order for that extra treatment.
If you worked at my facility, you'd not only be fired for that stunt, they'd most likely turn you in and try to get your certification pulled.