It is most likely based on the A72. Qcom purchased an ARM architecture level license, which grants it access to the design of ARM CPUs and allows it to make changes and sell the resulting product. This is what Kryo most certainly is.
This is how Apple started doing ARM CPU designs as well.
Not mentioned was that it doesn't inherit a lot of A72's quirks. For example, A72 has peculiar decode restrictions. It can only handle one NOP per clock, and NOPs somehow consume out of order resources beyond just a ROB entry. Kryo has none of these weird characteristics.
Plus original Kryo seems to be more than sufficiently different on pretty much every axis that if it -was- in part based on an ARM design I'm not sure how much of said design would be left.
(people curious about this should probably read the whole thing though since this isn't exactly my area)