You want to know how or do you mean why how this mod can be called "HD".
The Main/768p-Version has just lesser artifacts, is less noisy and the videos are in 60 FPS.
You need are video-compare-tool and see the videos in motion to see differences.
The 2K-Videos looks way better; but we can't use them atm.
So why is that, you may ask.
It's because the SotS-Source-Videofiles are

. No I mean literally overblown

!
Here on F95 you have the games like Ripples, Fresh Women etc.
The videos of these games, if we compare figures, need less but look so much better.
The SotS-Source-Videofiles have 6K-10K Kbit/s. Way too much for this blurry

!
It would be better not to try to remaster the SotS-Videos; but to remake them from scratch.
Believe me, I know how 3D-Graphics work. I doing that successfully for over 20 years.