What's wrong with this paragraph?

Here's a little tidbit from an article in yesterday's Wall Street Journal about a push for new restrictions on driving while using a cellphone.

In the accident, the 20-year-old driver fell asleep while talking on the phone, crossed three lanes of traffic and hit a car driven by a 55-year-old woman, who later died. Authorities lodged what they thought was Michigan's first cellphone-related negligent-homicide charge. Later, they added drug charges, after a medical exam allegedly turned up illegal drugs in the driver's system.

Tell me again how the cellphone was the problem in this incident?