Worth noting that the figure you show is not a LP thing, it was a Discord member exploring the map and labeling as they went. So I heartily agree the naming convention could be improved

and those labels also shouldn't be taken as definitive or objective.

And, to explain about why the clustering tended to spread out the Riptide cubes: if you check out "Cluster Details" you can see the cards which most differentiate cubes here. The Global cards are those which set the Riptide cubes apart from all 20K cubes -- stuff like Wharf Infiltrator and Archfiend of Ifnir. Budget cubes and "modal cubes" like to run these cards, too, and Vintage Cubes usually dont, which is why the Riptide cubes are near to explicitly budget cubes. However, the Locally Defining cards are what set Riptide clusters apart from the 15 nearest clusters (in this case, budget cubes and stuff), and those Local cards include fetches and shocks.

In other words, the algorithm sees some overlap between Riptide cubes and budget cubes, but then the Fetch/Shock manabase you mention is significant enough to warrant a separate cluster

Tjornan also wrote a nice article on the math which I'll link below:

https://luckypaper.co/articles/mapping-the-cube-landscape/