I can't tell from the video, but it looks like his foot may be on accelerator. While FSD Beta is active and you press on the accelerator it acts as a fast forward and will plow through signs and lights. The accelerator acts as a take over allowing you to get over dangerous situations where it may stop in the middle of the road.
That said, I've definitely seen it run stop signs, so it's not uncommon.
That said, I've definitely seen it run stop signs, so it's not uncommon.