You can’t know what is in front of the other car or why the Tesla braked. It could have been passing a slower car or truck (likely given the situation as described). If that car swerved a bit into the Tesla’s lane, braking could have been the right choice.

The car behind is always responsible for maintaining distance.

Realistically, if the tesla felt squeezed by a car it was passing, going a bit onto the shoulder would have been what I would have expected from a human driver. But no auto steering, tesla or otherwise, is going to do that.