The player is only categorized by association with the content they prefer to do. The content itself is what is categorized as 'casual' 'midcore' or 'hardcore' as determined by the amount of skill, effort, and time required to complete it.

If you primarily enjoy 'casual' content, then people will describe you as a 'casual player.'

Of course there are some people that use the term 'casual' as a derogative term which is just unilaterally shitty of them. Determining the difference between calling someone a 'casual' and them being a 'casual player' gets kind of screwy though just because of how people use the language.

If I call someone a 'midcore player.' I mean that they do most content in the game, maybe do a bit of EX or Savage lightly, but generally stick to what's majorly accessible to the largest chunk of the player base.

If I call someone a 'hardcore player.' I am typically referring to someone that engages in the most difficult content of the game and sinks quite a bit of time and effort into their completion.

If I call someone a 'casual player' they mostly enjoy low-effort content that doesn't require them to invest a lot of time into the game. Things like roulettes, fishing, gold saucer, etc.

I definitely want to stress that calling someone a 'casual player' is very different than calling them 'a casual.' Just like there's a difference between a 'hardcore player' and someone that's 'sweaty.' The latter in both examples is a demeaning people for what they enjoy to do, which, again, is just unilaterally wrong.