You don’t register in parking lots ...
He wasn't in the parking lot at the initial encounter. He was at the front door.
I've seen many voter registration drives like this. There's nothing wrong with them, as long as they don't try to promote a specific candidate, and they turn in all registrations.
In my state, registration is non-partisan. The only time a party is recorded is when you vote in a primary, so that you can't vote in another party's primary during the same election cycle.
He was registering in front of the supermarket. After I asked him about the Hillary logo, he got all apologetic and said he was done there. That photo in the parking lot was him getting ready to drive away. However, he was registering in front of supermarket.