A/C Unit + C02 Generator = NO OXYGEN?

I have a 15,000 BTU Window A/C Unit + 4 Burner Natural Gas C02 Generator in an 8x5 space... I was reading the manual for my Window A/C unit and it says

"Due to the possiblity of oxygen deficiency, ventilate the room when used together with stoves or other heating devices."

I think this was an old myth based on a mixed up idea that cold air holds less oxygen, when in fact cold air is more dense and therefore carries more oxygen right? Either way a search outside the MJ forums gets me oodles of people asking this question for the safety of their family and the answer seems solid. There is no process by which oxygen is altered in the workings of an airconditioner.