There's no way they couldn't find a trucker to use as a source due to DOT regs. Plus, drivers spend a hell of a lot of time waiting to unload, with the truck idling and them just sitting. I know quite a few truckers (personally as well as through my job) and you would be hard pressed to find a group of people more interested in having a long phone call.
I can't understate this, truckers will talk your ear off given half the chance and many of them will trade phone numbers and call each other to chat. Phone calls and podcasts are their main thing through the day, and I can't blame them. Yes, it's a DOT violation to fuck with your phone while driving, but it's fairly easy to preload podcasts to auto play before taking off and place calls using voice commands. Guaranteed the guy with the desk job has less time; freight brokers and dispatchers have high-stress jobs that require nearly 100% of time spent on the phone (you handle emails while talking to other people). Those are also high turnover, but not as bad as trucking simply because the hours suck less. Even local trucking is incredibly shit hours, it's not uncommon for it to be a 14 hour day when including stoppages.