In the Thatcham video, the "car" forming an obstruction is a dummy, and it's not metallic. I'd be surprised if it shows up on radar.
I'd like to see the exercise repeated with a layer of foil over the back of the dummy car, to give it a radar signature more like a real one.
That could've been a brick wall with this logic. I just think Tesla thinks it can apply agile development principles for self driving, fix bugs with software update after someone dies, and play with our life. I think it is closer to level 1 self driving than the "autopilot" or level 3 it claims to be.
The type of major obstruction which is by far and away the most likely to be present on a highway, is a vehicle, not a wall.
Nevertheless the problem here isn't the Tesla, it's the journalism. The test in the Thatcham video is so obviously, so deeply flawed, that it can only have been made to illustrate a point about "self driving" cars not being perfect
for a non-technical audience.
To anyone with the first clue about how autonomous (or semi-autonomous, or "assisted", or whatever) vehicles sense their surroundings, a test with a lightweight cardboard "car" is meaningless.
If anything, the Tesla did exactly what it should; crash into something it was able to detect as being insubstantial and harmless, rather than risk an emergency manoeuvre which could have resulted in getting rear-ended by another vehicle.