Joke answers and politically correct answers (its up to you to decide) aside.
Being "hardcore" in my OPINION is actively learning more about your hobby(in this case gaming). If just play you are a casual gamer, it doesn't matter what it is (angry birds to Dark Souls). But if you care enough about your hobby, to want to research more(ie visit the escapist) it means you are a hardcore fan. If you extensively research mobile games to see what is coming it makes you a hardcore gamer. The reason some games receive a "hardcore" tag, is because our casual brethren often don't hear about them and so do not have an incentive to buy them.
TLDR: It comes down to degree of involvement in your hobby (gaming in this case)
Being "hardcore" in my OPINION is actively learning more about your hobby(in this case gaming). If just play you are a casual gamer, it doesn't matter what it is (angry birds to Dark Souls). But if you care enough about your hobby, to want to research more(ie visit the escapist) it means you are a hardcore fan. If you extensively research mobile games to see what is coming it makes you a hardcore gamer. The reason some games receive a "hardcore" tag, is because our casual brethren often don't hear about them and so do not have an incentive to buy them.
TLDR: It comes down to degree of involvement in your hobby (gaming in this case)