The radial arm saw? Those are neat tools if you use them properly. The old use case documentation is written by sone hilarious evil genius.
Or did you mean the shaper he used to finish the cheeks? I think that was actually a giant router bit that looks like a blade.
This part. That bit just looks like a regular straight bit with no guide bearing. And I don't see anything guiding him parallel against the sides of the mortise.
Just kind of saying that I'd end up destroying the whole thing if I tried that (probably because I have tried lol).