It is to plug the hole, not a plug style door, though there is flexibility as to what marketing term is used. The same arrangement pictured here, on an Airbus, has been referred to as a plug style door.
The original design was true plug design, requiring passengers to manhandle the door from a sideways position back into the cabin. This was seen as a problem and seems to have been replaced with an outwardly opening door, hinged at the top and counterbalanced, that has an electromagnetically operated catch to prevent just this sort of operation. Since this wasn't intended for emergency evacuation I wonder if it had the top hinge or the catch. I suspect not.
Looks like a lot of forest to search to find the door. Start checking eBay and Craigslist.