A dive ops in Grand Cayman told me setting my Zoop to nitrox 21 was a different algorithm than air, and made the computer a little less conservative.
Just checked my Zoop in "plan mode" for both 21% nitrox and air. For 50, 60, 70, 80, 90, 100, 110, 120, 130 feet I got times of:
Set to 21% nitrox: 69, 50, 36, 28, 22, 17, 13, 10, 9 minutes NDL
In normal air mode: 69, 50, 36, 28, 22, 17, 13, 10, 9 minutes NDL
My Zoop doesn't seem to think there's a difference.
I have experienced this kind of behavior on occasion from dive op employees, i.e. making up nonsense in an effort to impress the customers with their superior knowledge of all things related to diving. I'll make an effort to chat with the nonsenser, swap IDC stories, try to find out how long they've been working as a dive pro.
My research suggests a strong inverse correlation between the time the person has been working and the amount of nonsense they're willing to generate and share with unsuspecting customers.