I admittedly find it a little bit confusing how many people here assign complete blame to exactly one participant.
The question is if in this case the action can be considered as deliberate. The "software" did it, is it deliberate? Is it considered as a failure of the car like the breaking of mechanical part?
This is new and the justice will have to figure it out and I am very happy not to have to figure it out.
I'd say there is only one car which did a clearly illegal action (sudden lane change followed by brake checking), so the guilt is 100% on them.
It's also true that the car behind probably could've been more assertive in braking harder to avoid reaching the Tesla (I wish there was a dashcam to see it from a better angle). But they didn't do anything illegal per se.
Also, that second car driver might've been worried of braking too hard to avoid getting themselves rear ended, which is a legitimate concern when having to break hard in traffic. Of course in the end they got rear ended anyway, but couldn't have known that prior to it happening.