It's a tough question to answer and it probably comes down to the individual's discretion. There is always the chance for cross contamination, but you can find Pseudomonas (and increasingly MRSA) almost anywhere (the shower is a great place to find Pseudomonas). Personally, I live life to the fullest. I do have a few CF friends, some of whom I have met in person. These people are healthy as well and if they do culture something, it's generally pan-sensitive P. aeruginosa, which is what I culture as well. I don't think I would spend a great deal of time around someone who cultured a more insidious, hard to treat bacteria.
Unfortunately, it is not always easy to tell exactly what you have growing. Myself, for example. I have never been able to produce a sputum culture on demand. The only time I have a productive cough is if I am getting sick, so we rely on throat swabs. You never know though if you might be growing something deep in the lung and it's just not showing on the throat culture.
Speaking with his doc probably won't help either as they will err on the side of caution.