I think the whole driving while "distracted" issue boils down to the type of distraction. My two cents...
ACTIVE
A phone call is an active engagement. You talk. The other person then talks. You are expecting feedback, so part of your brain is tuning in to receive that potential incoming response, therefore causing some people to not focus on other activities (such as driving).
Another example would be texting. You get a text. You actively look at it, then respond back.
PASSIVE
A horrible song comes on the radio. You slightly lean forward and turn a physical knob or physical button to change the channel. You are not expecting further input form the radio. You just want it off of what is on there now.
Another example would be turning the heater on/off. You just lean over, grab a dial, and turn it down. You are not expecting feedback from the heater other than for it to get hotter/colder. No unexpected feedback.
Another example would be eating a hamburger. You have the hamburger in one hand and driving with the other. No need to look down at the hamburger or listen to the hamburger, it just is passively being eaten.
Talking to another person IN THE SAME CAR could also be seen as passive. You are not trying to dial someone. You are not trying to hit a button to respond. You are just opening your mouth and talking. Those same systems that allow you to talk are not tied up with hand-eye coordination of driving. To counter that, if you have two kids in the back seat and they are fighting causing you to look up into the mirror while you talk, then that would switch to active and not passive.