People use "capitalism" in different ways. The person you responded to probably meant it as "free marked system", which Lemmy absolutely fits into. Often "capitalism" is used to mean "profit seeking system", which Lemmy doesn't fit into.
Both of these uses are common.
Idk if you are trolling, but in most cases 0 is considered a part of the natural numbers. And there is a huge difference between the naturals and the integers: the naturals are for induction, the integers are for algebra.