How was the saturation measured? Pulse oximeter or arterial blood sample?
A pulse oximeter will give a falsely high reading in the presence of carbon monoxide in the blood due to its colour (bright red). The pulse oximeter measures the saturation by measuring the wavelength (colour) of the blood passing between two diodes, basically. Therefore, if you have a significant amount of CO-Hb and an arterial oxygen saturation of 70% then the pulse oximeter might indicate 100% saturation anyway.
As an aside, Methaemoglobin has a colour which gives a reading of approximately 85% using a pulse oximeter, so if you have an oxygen saturation of 60% that might give you a falsely high reading in the presence of Methaemoglobinemia, and a falsely low reading if your actual oxygen saturation is 100%.