The crazy high numbers are due to a fairly Microsoft-specific definition of "API" in this context. What they count here is class members; so they ported a class with 15 methods and 3 properties, they'd count this as "18 APIs" (or perhaps 19 - not sure if the class itself counts as an "API" as well).
That being said, I'm sure there was indeed an impressive amount of code that had to be ported.