I was rear ended and told I’m at fault (CA)

So I was rear ended yesterday.

I was getting on the freeway with a meter, but the meter was green and not changing. There were a lot of cars in front of me, but one car in the line decided they should brake, even though the light hadn't changed for any other car.everyone stopped, including me, who was paying attention. The car behind was not paying attention and rear ended me.

He admitted fault to me and his insurance company. Not that that really makes a difference BUT I received a call from his insurance this morning stating that they were taking the fault and paying for my damages. Ok cool, just as I thought it would play out.

I just got an email from my insurance, stating that I was at least 51% to blame for this accident because I was "traveling at an unsafe distance". WHAT?? Someone please explain this to me… this email came at 10:20pm PST and I can't just call someone to talk about it. I left a voice mail with the claims person with my insurance that I've been working with.

Why would me insurance say I'm to blame when 1. The other company/driver already took blame and 2. I was stopped and paying attention, and the other driver obviously was not!