It really is just a big guitar.
The band had some success with a YouTube video of themselves performing the song "Red Hands" in which all 5 of them played one normal-sized guitar.
Later they put the same song on YouTube, this time performed on the big guitar.
In the YouTube description, they write:
We found this MASSIVE guitar at a pawn shop....the rest is history!
So the provenance of the guitar probably isn't available - but we can assume it was built as a novelty item. Maybe for a shop display, maybe for a novelty stage act.
There is some precedent for enormous, playable, guitars. The 1991 Guinness Book of Records says that this one in Australia is the biggest. By now it may have been beaten.