To simplify, this is achieved with an "anamorphic" recorded image.
(like the "5K preset" in Danne's build or like in this video where he uses the Canon 700D, it's with Bilal's build)
But to clarify, you are not necessarily free of aliasing. In my experience this depends of the process used to "desqueeze" the image.
For example if you are using MLV App, or DNGs in Davinci Resolve... the scaling algorythm is different and the result will be different too.
TBH I'm watching the youtube video with a 4K monitor and it was aliased anyway, but sure very much less in the shots in 1x3 than 3x3, but moire still present a little bit to an advised viewer's eyes.