yeah, I expect they use the camera as a make-shift ambient light-sensor, just with a lower frequency than a illumination sensor would be used (due to power consumption impact), and with overall lower accuracy (lower dynamic range, reduced FoV, very bad accuracy in low-light/bright conditions,...).

This pretty much matches the described experience in the article that Gruber had, as he mentions he had to adjust brightness up and down at least twice every day...