You did the right thing. I would find a charger for #1. Also the value of the phone matters. I would not expect someone to drive 40 miles and risk getting mugged by a stranger to just to get a prepaid phone with $5 left on it.
They are probably just trying to be cautious. The one could have been stolen like you speculated or they just thought it was stolen.
I've found two cell phones so far and simply dropped them off at the closest retail store for the respective carrier. The store personal seemed appreciative and promised they'd get them to the owner. If I ever loose my cell phone, I hope someone will do the same for me.
I would want to take matters in my own hands, because the carrier employee could just keep the phone, and do nothing. There is no accountability.
I like the idea of not meeting the owner directly, taking it to a grocery store, but when the owner arrives, the person at the store could say, "What phone? You must be mistaken." Probably fine if it is not valuable, but if it was the latest $700 smartphone, I want to meet them. You could tell the owner what employee you talked to, but they could still deny it.
I would be afraid that a government employee like the police would put it in a box to rot and not afford any effort or diligence to find an owner, whether due to bureaucracy, too many cases, risk of getting fired for what could go wrong, thinking that the owner should come to them, etc.
Found a few at the beach...the last one I was going to call the info number, but took a nap instead after getting to the beach at 0430 AM...next thing I know, someone is knocking on my door wanting to know if I had their phone..they tracked it to my house..wanted to give me money, but didn't take it...nice return..Buster......
What kind of phone was it? The owner sounds tech savy, has money, offered a reward. Could have been the next Bill Gates, LOL!