How are those the same? You need to define "religion" and "sport" rigorously first.

This is really the crux of the argument. There are no absolute authorities on religion, sport, or in the case of the original post, mathematics. We can have definitions by general consensus, but they are rarely universal and thus it's easy to cherry pick a definition that supports any particular argument with no ability to appeal to authority.

I have no idea what you're on about with not golfing being a sport.

It's mostly a troll argument, but you can easily trip up people with interchanging the definition of "sport" as a thing ("golf is a sport") or an activity ("playing golf is a sport"). Then after trying to hammer down the definition more exactly, you can often poke holes in it with more questions like is chess a sport? Is playing Counter Strike a sport? Is competitive crocheting a sport? All of these ambiguities are possible because of the lack of a universal authority in the realm of sports, though some people try to pick an authority such as the Olympics to prove their point.