By reading between the lines, of course. As with most news reports of vehicle collisions, there is not enough information presented to draw an accurate conclusion. However, experience tells us that the liberal media tends to spin the "cause" in certain ways, i.e. calling it "speed related" or noting that a deceased victim was not wearing a seat belt - so they filter the information they provide in order to support their own preconceived notions. You'll notice they don't say what the result of the driver's blood test was. Did he have any alcohol in his blood, or was that "strong alcohol smell" simply the result of a bottle of legally-transported liquor being damaged in the crash?
It's a guess, but a pretty safe one. Most Sloths are so totally oblivious to their surroundings that they wouldn't notice the collision. Or, since they weren't "involved" in the collision (i.e. none of the other vehicles actually struck the Sloth) he figures he's not required to stop.
I disagree. There is not enough information presented to either prove or disprove any conclusions regarding cause. My hypothesis is as good as any other right now. It's certainly as good as the insinuations of a slanted news report from the liberal media...