Hit and run is a felony, especially failure to stop and render aid, while DWI is often still a misdemeanor. Not saying the dude was necessarily knowledgeable about that or weighing those options if he was intoxicated at the time.

One of the posters also claims to have met the suspect and attributes the "smirk" to some sort of skeleto-muscular deformity, though it's hard to determine validity with anonymous internet posters.