In my opinion it needs an exeptional talent with litle efford. For example a 9 years old kid wining games againts titled masters and the kid saying something like: "i just learn this like 6 months ago by watching my grandfather and his friends when I visit his home last christmas"...
In the other hand if you have someone with 2700+ and says it toke him years of hard work and dedication to get there, then he is not a genius.
For example, would it be 2700+? Do people normally call these players "geniuses"? Or, might it be all GMs?