A developer can take an educated guess at how the functionality is implemented. A lot of software problems have a single sensible solution (and that's why software patents are bad). Either Apple has used NSDate (as stated - a public and widely used API) or has reinvented in the wheel. The former seems more likely, though the latter would explain why Apple has been the victim of so many end-of-year bugs.
Apart from the fact that there are more than two possibilities involved, he still doesn't know what he's talking about.