This happend on a highway. The Tesla switched lanes into oncoming traffic moving faster than itself. It immediately started braking for no reason. On top of this, it all happened in a tunnel entrance.

Yes, you should remember that vehicles can suddenly stop. This means keeping a safe distance from the vehicle in front of you, and looking beyond that vehicle to anticipate what is going to happen. However, a vehicle illegally throwing itself in front of you and doing basically an emergency stop because it just feels like it is not something a reasonable driver is expected to predict.

If you look at the video, you can see that the first vehicle is almost at a full stop when it hits the Tesla - its driver performed as expected. The second vehicle comes to a full stop before hitting the first one, so that's also going quite well. The third vehicle (a rather large truck) doesn't brake but instead swerves into the other lane, almost hitting another car. This dooms vehicle number four, which suddenly finds itself mere feet away from a stopped vehicle. Five through seven are tailgating and never see it coming for the same reason. Number eight is able to stop in time.

The speed limit here is 50mph. Assuming they were driving the speed limit, the typical stopping distance would be 174 feet. I can assure you, nobody keeps a distance of 174 feet between them and the car in front.

In this case the Tesla stopped because of what you might charitably call a breakdown. This would probably get you out of the dangerous driving conviction but if it happened multiple times would probably result in a recall on the vehicles to fix or disable the faulty part.

The longest delay on a motorway I've ever had (get out of the car, walk the dog, hang around for a couple of hours in 32C degree heat) was a case of a driver of a small car having a heart attack, slamming on the brakes, and getting rear-ended.

The car ended up half it's length.