Yeah, it's pretty clear the driver is the actual SCP. There are multiple pizzas so it's not that. It's not the process somehow because otherwise other drivers would be affected. It's just this one guy so he should be the main SCP and the pizza is SCP 3275-2 as the pizza is influenced by the delivery guy, not the other way around.
TL;DR This SCP could be titled the Pizzas of Dorian Gray. It wouldn't be accurate but that's what you get for not reading