Moon, COTD, Liberty Falls, Der Riese, etc something tells me
The fact that this and in PVZ2 Crazy Dave and Penny (Time traveling car that has an advanced AI on the level of COD zombies AI machines) had a similar story to the Ultimis crew tells me that the PVZ universe might be an alt universe inside the COD zombies multiverse.
And that crazy Dave is actually his universe version of Richtofen.