Some people who play piano for, let's say, a year [18 months, two or three years -> in all cases a relatively SHORT period of time] claim that they've "mastered" pieces such as Moonlight Sonata third movement (most frequent), Prokofiev Romeo and Juliet or preludes and fugues by Bach. Sometimes they even don't have a teacher or play by the ear!!!

Some also claim to have finished 7-8 grades in one or two years... What do you think of them, and how is it possible that they manage to actually play those pieces?
In my country we have:
-primary school (grades 1-6)
-secondary school (grades 1-4)
-conservatory (grades 1-4)
=all summed up - 14 years!!!
You don't even think of attempting, for example, preludes and fugues, Prokofiev Montagues and Capulets or Moonlight third before second or the third grade of the SECONDARY school (before having played piano for at least 7-8 years). So are there really people (and not just those rare, extremely hard-working and gifted exceptions) who "get it" that easily? If yes, HOW DO THEY DO IT? What's the quality of their performances?
I'm really puzzled by this one... Are they most often those shallow people who play piano only to impress others and thus gain respect, the ones who don't really enjoy classical music or play some "pop" songs to be considered "cool"? Please, give me your opinions! Should they be respected or not?
P.S. Use the search button, you'll find plenty of posts like: oh you don't need to spend 7-8 years to finish grade 8.... Well, I've just finished them all in two! ...and similar...
Thank you all, A LOT!