The accident was horrible but also weird. Biking on the sidewalk? next to a highway?? With turns??? It just reads bizarre and like a traffic system that is very hostile to anything but cars.
As someone who has lived in Oregon, I can say that I don't find that accident very weird at all. Although Oregon has some of the best biking cities in America there are still many places even in the Portland metro area where bike infrastructure is almost completely nonexistent, forcing you to either ride on the road or on the sidewalk.
Some people just never feel comfortable riding on the road and will opt for the sidewalk because it feels safer for them, and sometimes it is. (Hopefully those people are minding their speed and being aware of pedestrians so that other people feel safe too, but that's another story.)
And of course there are "stroads", as the urbanist geeks call them, which are something between a highway and a road. On these kinds of roads you'll have cars driving relatively fast, turning and changing lanes often to get into various shops, as well as people walking and biking all over the place.
When I think about this accident I can easily imagine something like it happening on a "stroad" like Beaverton-Hillsdale highway in Beaverton, OR (a suburb of Portland), because it's a main artery through Beaverton, full of cars and people all of the time, has tons of access points for turning into shops, tons of construction all of the time, bad street lighting, and of course... no bike lanes at all.
On a street like that I can easily imagine a person, especially a kid without a lot of biking experience, feeling like it would be safer to ride on the sidewalk and then getting hit by a car that decides to quickly turn in to one of the various businesses. So, yeah, it really is a failure of urban planning more than anything.