Allow me to tell you why you're wrong.

driver's speed

Math, by using the size of the sign, imposing it on a fixed distance and measuring the time it takes the car to cross that distance we can see the speed of the car. It's reasonable to assume the car was going faster than when it entered the frame as it was braking the entire time and 40 is a nice conservative estimate, regardless they would have hit the kid no matter what value you substitute.

speed limit in the area matters as well.

Yes it does, but there are very few places that have speed limits below 30, and regardless, without actually knowing the speedlimit you can't pin blame on the driver.
From the facts we can currently deduce, the skater was entirely at fault.

I also liked that you felt proud enough to use this same comment multiple times in this thread.

dude did the work, and when he sees somewhere where the comment is applicable why not repost it again, given how massively downvoted the parent comments are it's likely very few people will even see this.

To conclude, with the facts we know, the drivers degree of fault = 0, now I'm not saying that can't change, if it emerges that the speed limit was 30 then the driver was breaking the speed limit, although whether they would have stopped in time at 30 is anyones guess.
But here's the clincher that really keeps it in the drivers favour, stopping distance and times get tossed out the window when a pedestrain purposely puts a driver in a situation where they need to perform an emergency stop if I measure the distance it should take a competent driver to stop given the speed limit, then step out infront of a vehicle that is exactly that distance away I am in the wrong when I get hit, regardless of what the vehicle does, the skaters actions amount to no less, he emerges from a blind corner at speed without checking for vehicles coming from the direction he can't see.