It didn’t actually.
21:44.5 44mph. Starts slowing for the red light.
21:46.5 41mph. No problems obvious. Still slowing.
21:47.5 38mph. At this point an astute human driver might have detected an issue due to odd trajectory. Car still slowing gradually.
21:48.5 35mph. A human would definitely know there is an issue; the Bolt is now nearly head-on (image below). Still gradual slowing.
21:49.5 32mph. No response. Normal slowing.
21:50.0 30mph. 1.5 seconds since an obvious problem, or 2 seconds for an astute driver.
21:50.1. 28mph. The car has definitely started to respond, slowly.
21:50.5. 24mph. Increased rate of slowing, definitely in response to the Bolt. It's been 2-2.5 seconds since a problem was detected, depending on alertness.
21:51 17mph. Much more rapid response (finally!). It's been 2.5-3 seconds.
21:51.5. 14mph. Finished slowing, Bolt has started to recross double yellow lines and is no longer a danger.
So at least two seconds to respond in a meaningful manner to a clearly oncoming car. It wasn't a crisis, but you'd expect better and earlier to allow plenty of margin. That's what computers are for! They should be faster than humans (it would take a human about a half second to be on the brakes hard). I think this is a pretty bad showing; this is why we have safety drivers who should disengage immediately when something like this happens (and in fact this is one of the major risks of FSD - in this case it clearly
increased the risk of a collision). I think FSD didn't respond quickly because there wasn't really imminent danger, but the prudent and human thing to do would be to slow down; the Bolt could have been trying to create a Bolt bonfire. But in any case, the Tesla didn't brake immediately. And it did not make use of the perfectly good right turn lane, which a human would have done to virtually eliminate any possibility of collision.
People are right to doubt these two beta testers. They're very bad at what they do (unless you're talking about monetizing YouTube). Don't believe everything you read on Twitter.