IIRC it made extensive use of lookup tables, both building them and being driven by them.
It wasn't a complete implementation, but it proved the theory and scratched an itch.
I can see what you mean about it scratching an itch. Definitely piqued my interest!
(Varying "citation needed" didn't quite convey genuine curiosity the way I thought it would.)
What I would bet a respectable sum on is that you can't parse/process/interpret even the simplest recursive languages (e.g. arithemtic, Expr ::= Expr + Expr | NUMBER) from pure Excel. Forget expressing the algorithm, there isn't even a suitable data structure to iterate over.
Here is a video of a doom-alike in excel, explained by someone with a bird on his head. He's not clippy, but a real person with a bird on his head. [1]
Here is a video displaying a walk-through of the Excel easter egg that showed the Hall of Tortured Souls! [2]
There was a Windows 95 screen saver that was Doom like though.
95 had the “Hall of Tortured Souls”—a 2.5D first-person walker—which was more Doomlike.