When you view the almanac and go to Pumpkin’s entry, it reads,
“Pumpkin hasn’t heard from his cousin Renfield lately. Apparently Renfield’s a big star, some kind of… what was it… sports hero? Peggle Master? Pumpkin doesn’t really get it. He just does his job.”
This means pumpkin is related to Renfield, and subsequently, canonically part of the PVZ lore.