Confusion about isotherms

LED Flashlights – General Info
1

I’m learning about the different types of isotherms, and I found this chart

However, I see that the isotherms used here are sloped the other way

What is this type of isotherm called and why is it so different? Which type of isotherm looks more like the same CCT?

2

They’re the same but on two different color spaces, the first is CIELUV and the second is CIE XYZ

Edit : since the coordinates are u v instead of u’v’ then it’s CIE 1960 for the first one.