Kidnapping logic

So our fam thoroughly enjoyed the long four day weekend -Monday was the first full day I've had with the kids in a LONG time - and it was a joy. We headed to Chick-Fil-A and while sitting in the drive through, Eli, taking an especially friendly turn, rolled down his window and waved hello to a woman crossing the parking lot with her 4 kiddos and a baby stroller tow.
In an unusual reversal of roles for the two of them, Julia was mortified.
"Eli! Stop it! You don't even know them!" she scolded.

"What?!? I'm just being nice?"

"Yes, but they are strangers. How do you know that they're not kidnappers?" Julia warned.

"Well, usually people with that many kids aren't really looking to take any more, " he replied.