That specific run was recorded with a version of PrBoom+ that allows for constant SR50 (which is straferunning with both the strafe buttons AND arrows with strafe on - it would be period plus alt plus right arrow with the standard setup - normal straferunning is just SR40) and like myk said, the ability to continue from any point in the demo if he stuffed a bit up. There's more on his Doom Wiki page.
RamboBones holds the current record for Doom 2 UV Speed TAS runs at 14:02. Entryway still well and truly holds the record for the same on Doom 1. His Doom 1 runs are approaching 5-minute-Mario perfection, I don't expect we'll see them beaten, and if so only by a few seconds.
Apart from shitty old games, I also love speedruns :)