Normally the developers wouldn't classify images themselves (their time is too valuable). In any case, I think failing to detect a face as human should be rare unless the photo has very poor lighting or the person is almost hidden.
Your expectation was the same one they had, and it was wrong, which is the crux of the issue.
Do you have a source for data set mis-labelings being a problem?
If you asked the developers of the facial recognition library, "does your software have problems with very low contrast conditions" they'd surely have answered yes. Fully conscious of the issue but, that's software. It's hard to get everything right 100% of the time.