Therein lies the puzzle. I suspect he'll never get a straight answer - what they say to him and what they type on his notes on their computer could be two different things - they'll probably put him down as code XXX which will mean "tell him he's not at fault but try to load his premiums anyway by talking about the volatile insurance market due to the recent air strikes on the militants..."
I'm pretty sure that's what they did to me when I had my claim - dashcam proved me innocent 100% but my premiums still went funny for a long while.
Depends who you were with. Some insurance companies will still load you for none fault claims as its still an increase in risk according to their risk / pricing algorithms.
Whats important is how liability is settled on your son's insurance record and how it will be recorded on the CUE database by his current insurer, as this will affect him when it comes to swapping insurer at a later date and how they note the claim on their systems when quoting.