Didn't one doctor who examined some of these people describe damage that looked like "a concussion without a concussion"? I.e. damage to the brain you'd see on people who had conxussions, but they experienced no physical trauma?
A psychological cause absolutely could have physical effects. It'd be really hard to develop an ethical experiment to test if these specific injuries could have a psychological cause, but other damage has had such a cause.
Also, like two people had concussion like brain scans without knowing they had a concussion. They could have just unknowingly had a concussion, it's not like they had brain scans before and after the "attack" to compare.
This would have been part of the evidence the panel ruled could fit a psychological cause anyway.