I can understand what she meant.
I have a good ear, very good memory and a high capability of learning a new skill.
I taught myself about 22 years ago.
Some of my "repertoire" was Complete Beethoven Op.27/2, movements from Op. 10/3, Op. 13, Bagatelle Op. 126/4, Chopin Preludes 4,6,15 and 1 or 2 other things I can't remember.
I thought they all sounded pretty close to the recording I heard.
Then I stopped for about 12 years and started proper lessons 5 years ago.
I can now play fewer things, but the music in them is so much better.
I understand the music better. The tiny changes in warmth and colour make a HUGE difference in how the music sounds.
But even now, when I think a piece I play is good, my teacher will still say no, show me the technique, make me play a different way and the difference is immediately audibly evident to my more trained ear.
I would certainly not write off her comment. Even my teacher who was a concert pianist winning many local competitions (And her students as well), said that she has attended masterclasses where the teacher hears something where she can't. But 30 minutes later the student's piece sounds better. So I believe there are just levels of musical accuity that are much higher than one would normally think of and stringing together all the sounds a piano can make in the right way to be musically significant is not as easy.
And judging by the amount of nasty criticism often levelled at the top pianists, most people know it.