There is an important distinction thats developed.
Being nerdy/geeky, used to be associated with being heavily interested in a niche topic, could be anything from astronomy to maths, to chess to jigsaws... the kind of people who developed these interests also tended to very introverted and be into certain (often solitary) subcultures - comics, roleplaying, science fiction, sometimes music. In this paradigm its possible to be nerdy about anything - its a mindset rather than a set of interests.
Nowadays, being nerdy just means the latter, shorn of almost any other factors, so its a classic mainstream co-option. Take the surface level, repackage, and sell it on as something desirable. So essentially, being into nerdy 'stuff', doesn't really have anything to do with being a nerd anymore.