Check out the interface screen, specifically from 0:17 to 0:21. I think the navi is operating in a developer mode. It shows what the FSD senses.

Interestingly it seems that it does accurately sense the lights for a moment. But it also erroneously senses them, and the flicker pattern means it probably wasn’t able to come to a confident determination. If that’s the case this thing should have been built to fail safe.

As the operator states, that’s a highway. They were taking quite the risk to chance it a second time, which is the iteration captured on video.