If we’re speaking minimum I’d say the person is at least an “advanced user”, possibly implying they’re naturally gifted for it as well and can develop and evolve that specific talent at a faster rate than the average person would.

As for the latter question, I’d focus less on what I think about myself and more on feedback from others. If they say you’re “good”, even if you don’t define yourself as such, chances are that you are good. If you weren’t they’d be much quicker to judge and criticize you.

People are different, and have different tastes and predispositions. No one is “good” at everything, and everyone has some kind of hidden talent, no matter how useless it may seem in some contexts. And some stuff even if you’re not naturally talented (I.e. basic living skills such as cooking, basic DIY fixing or cleaning) you should always strive to learn enough to at least be an independent person.

That’s basically how I feel, and as someone who once tended to undersell himself while most people praised my skills a lot and came to me for help regularly on tech-related stuff. Some even get hateful over how fast-learning and adaptable I can be at stuff I like to do, since it tends to be rewarding and fast-tracks me to a better life standard.

Still, humbleness is always a good trait, and often appreciated. At the very least better than being overconfident and making a fool out of oneself by attempting to swallow more than one can chew.