Supratherepeutic referes to an amount greater than is required for a therapeutic effect. E.G. if a patient only requires, sticking with O2 here, 4lpm to see an improvement in their status, and you administer 15LPM, then you have administered a supratherepeutic amount of O2.
Supraphysiologic is similiar, but refers to an amount greater than what your body can or will use.
This is something that you need to ask yourself. Also, look at the other vitals. What do the lungs sound like? What is the pulse rate? What is the blood pressure? SpO2 is helpful as long as it is taken into context. Certain conditions such as anemia, shock, smoking and even being cold can skew the data it gives. Also, it only reads the saturation of whatever molecule is bound to hemoglobin. This means that if the patient had carbon monoxide poisoning, the SpO2 could read 98. Of course in that situation, O2 would be needed.
I would never withhold oxygen for a patient that wanted it, but, from what you described, the patient showed no signs of respiratory distress. Giving O2 certainly would not have harmed the patient and it would have been a very prudent measure to take, but I don't think you are in the wrong for not giving it. My point is that it is important to look at the patient and not the machines, you can make your decisions from that.
