How exactly has Diamond ore generation changed in 1.18?

The recently released "Caves and Cliffs - Part 1" update is version 1.17. This is what the hermits are playing in season 8. Here is the official information from Mojang about splitting the update in two parts: https://www.minecraft.net/en-us/article/a-caves---cliffs-announcement

The diamond ore distribution is not changed in 1.17, it is still a uniform distribution in levels 1-15. However, there seem to be some incidental changes because of world generation changes of other elements around these levels. Here is a video that shows a comparison:

The confusion is due to the upcoming (fall 2021) "Caves and Cliffs - Part 2" update, which will be version 1.18. There, the distribution of all ores will change significantly. Mojang have shown what exactly they intend to change, that is why on the internet there is a lot of information about 1.18 even though it is not released yet. Of course, things can still change significantly before the final release of 1.18.