But it's only a 'straight rear end hit' if the person in front DOESN'T admit to any sort of role in causing it. If you tell the officer 'that [insert rude name for person] behind me was too close so I figured I'd show him and hit the brakes' w/o making up a ground squirrel, phantom vehicle or pothole or something quasi-real to have stopped suddenly for, you can be liable. I do agree that the rear ender should bear the majority of the responsibility in most cases but in a small percentage of cases, it can be 50/50 or even more the fault of the guy to the rear.
There's an interesting book about insurance fraud called "Accidentally on Purpose" which explains the actions of a ring in California which had an m.o. of stopping suddenly in front of car transporters, which carry high liability insurance amounts on them. This worked profitably until a trucker stopped hard enough to break the chains holding the car on the top of the cab and it fell off and smooshed the dudes in the car. W/ fatalities, they reconstructed it and found the car to have been at fault (and turned up their histories of similar losses...) and the crooks didn't get squat. That's certainly an extreme case but we still don't know exactly what he told the cop.
If he told them he did something for no reason other than that the person behind him was annoying him, he could be at fault. There's laws against that in some places. Again, we don't REALLY have enough info to say for sure but this is an odd case. In the state where I live (and investigate accidents...fwiw...) you can have that situation, they are EXTREMELY rare and in the VAST majority of losses of this nature, it is entirely correct that the rearender is found at fault. It is so unusual that the rearendee was cited or in danger of being cited here that I have to suspect that he perhaps said too much to the officer and incriminated himself somehow. Just a hunch but the fact that she wasn't cited after they went through all the shenanigans of tracking him down makes me think that he said something perhaps that might have been better left unsaid.