Bob has so many uploads that I'm not even going to attempt to look for it there.
What I believe I saw, was a table mounted router with a saw blade, not a slot cutter. I'm guessing the blade had 20 - 24 or so teeth.
Since I didn't have a use for the setup at the time I saw the picture, I didn't really study it such that I can tell you for certain what I wrote above is what was in the picture.
I've never built a box, so it didn't occur to me that one would build a complete box and cut it open as opposed to building the top and bottom separately. I also remember thinking that this method would make for a perfect fit of the lid, and that the thin kerf of that blade along with the solid foundation of a table and fence, would make for an even cut without removing much material.
Now, based upon that memory, I'm fairly certain I saw what I have indicated above.
However, if someone were to challenge me to a bet that what I saw wasn't actually in the picture, I wouldn't take the bet.
Buy I really really think I saw a saw. :"^)
You think I'm crazy? Wait till you meet my imaginary friends.