Pretty sure that was meant as a joke.

Mouth breathing is not a cause of sleep apnea, but it can be a consequence. Bad pillows and bad sleeping positions aren't causes of sleep apnea either, but some people do have "positional sleep apnea" where the apnea is (usually) much worse on the back and much better on the side.

One can also have sleep apnea without ever experiencing hypoxia. Drops in oxygen saturation during hypopneas are very minimal, and pretty much nonexistent with respiratory effort related arousals (RERAs). Not breathing is bad, but for many people with sleep apnea, the problem is the constant arousals and the lack of decent sleep, not a lack of oxygen.