That function takes no argument. I've never seen initializing a single variable and returning the result of that initialized variable from a function call taking no argument called "memoization".
Memoization is a specific type of caching with a space/time trade-off where the result of a particular (set of) input(s) are cached.
I find it quite a stretch to call initializing a single integer for a function taking no parameters "memoization". I'd just say the function's return value is "cached".
I mean: by kinda, sorta, bending the definition of memoization (for example by changing "caching the function's results based on the inputs" to "caching the only result for there's no input to the function") you could say that it is actually memoization but then I'd argue this is not a great example of what memoization is.
I may be wrong though.