The author of that blog post would offer us that anything we do is completely modular--that anything can be switched out for anything else, because everything is simply the result of a decision.
So, if you have a hobby, it can be switched out for any other hobby and you would be just as interested and fulfilled because it's all just a decision. That you have an inclination for advanced math puzzles and no interest or ability in sports is immaterial--you can replace the time spent doing math puzzles with time spent playing rugby and get as much fulfillment. It's just a decision, remember.
There are some people who are truly monogamous and have only one mate for life, never considering anybody else as a potential partner. There are those who are serial monogamists who never consider anybody else while still involved in a pairing. There are serial monogamists who are always considering options while still involved in a pairing. There are poly folk who have a couple of relationships and never consider more. There are poly folk who have several relationships and are open to yet more. There are folk who never have any serious relationships and just bounce from one sexual dalliance to another. To suggest that the whole range of human behavior regarding relationships is due simply to choice and anybody displaying one of those forms of behavior would be just as comfortable displaying a different one is ludicrous, at best!