The old notion that sensors always go bad in cars was never really accurate. People would see a check engine light, get the code read and see it says "O2 sensor" and replace the O2 sensor. Then the code happens again, they say "That damned O2 sensor on this stupid car" and replace the O2 sensor again. Rinse and repeat until you get a new car.

However, I'm willing to bet the O2 sensor was actually giving the correct read and was working fine, and the source of the issue is probably well upstream of the O2 sensor.