Hello, video creator here. This is indeed the actual code, and it is written in QuakeC, a language created specifically for the game logic in Quake. The part I'm not sure about is why the creators wanted to add in extra side beams at all.
So both the "normalize" and the improper swap are the part of the original source?
https://github.com/id-Software/Quake/blob/bf4ac424ce754894ac...
:)
I haven't played Quake in the better part of 20 years so I can't comment from first hand experience, but judging by your top-down view at around 41 seconds, the single beam visually seems to intersect with a bunch of enemies while not dealing any damage (probably as a combination of narrow hitboxes on both the beam and the enemies).
https://www.ryanliptak.com/blog/rampsliding-quake-engine-qui...
Especially with games, I think the video format lends itself well to demonstrating the effects of the code organically.