It's criminal because he disregarded traffic signals (I believe he recently pleasded guilty BTW). It's also negligent when he gets sued by the decedent's relatives in civil court.
That's not the app's fault, but it's not the only case where people have got into accidents because they were pursuing the status of fastest rider on a particular route. Where rewarding people (even intangibly) encourages them to push up against the limits of safety/legal restrictions, there's an argument for proximate causation, eg 'but for Appmaker's reward of an exclusive title (King of the Mountain) to the fastest cyclist on that stretch of road, Cyclist would not have habitually ridden at such high and dangerous speeds.'
It's the app equivalent of a "cannonball run" - a race to see who can get from point A to point B as fast as possible. Unless you have some way to ensure participants obey traffic regulations (and I don't think anything exists at present), if you base winning on minimizing time you are arguably inducing people to break rules, since that's almost mandatory to win.
There's still some rallies around that run on public streets, but usually winning is based on _matching_ some target time, rather than having the shortest time overall.
Riding a bike fast is not all that dangerous. Ignoring traffic controls is. One would expect that the "king of the mountain" rating is based on a combination of lucky traffic light timing in addition to raw cycling skill. Otherwise, Lance Armstrong would win every route, right?
