This comment was clearly made by someone who has never practiced art or music at a high level. You are trying to compare your experience as a musician with someone who has worked toward and dreamed of being one of the best there ever was since some time in, most likely, early adolescence.

I was among the best in my year on my instrument in the country. I went to one of the top music schools in the world, and then I moved to New York to keep studying and start working as a musician. Some time in the middle of the financial crisis, I got tired of being broke all the time, and of constantly battling injuries (that's thing you've probably never had to worry about, as an amateur musician. Your arm is sore? You get to take a few days off!), and teaching music to the spoiled children of the masters of the universe. I learned to code and started working as a programmer.

Everyone who has ever been among the best, but didn't quite make it, has to, at some point, decide they didn't make it, and quit. Once I quit, I barely touched my instrument for two years. Playing when you're out of practice can be pretty painful to someone who is highly trained. You've worked for years toward perfection and then you just have to start accepting... less than that.

Here's another thing that happens when you quit: you have a constant voice in the back of your mind wondering whether you gave up too easily. You were there with the best people in the world, and now you watch them take their place among the leading lights of the art, and you can't stop picturing yourself among them. It's not whining, it's the painful experience of giving up your lifelong image of yourself. Being a musician, a top level, professional musician, dominates your whole identity. Try to imagine this: rather than finding out at an early age that you're not the next Jimmy Page, you get very good very quickly at a young age, and people start telling you, hey, you could be the next Jimmy Page. You work for decades to get good enough, sacrificing your personal relationships, your childhood, choosing over and over again to stay in and work instead of doing whatever else you could be doing, and then at age 30 after years of near misses and barely scraping by, you realize you're just not the next Jimmy Page. It's not an early realization, it's a gradual defeat. And it's devastating.

Regarding imposter syndrome, there have been studies of musicians using the standard "sandwich method" of delivering criticism, in which the criticism is sandwiched between two compliments. Trained musicians often don't hear or register the compliments at all. I had this experience with my girlfriend recently. She played some excerpts for me, I said, "wow you sound great, I liked X and Y. Here are a few things you should work on." She asked me later if I thought she was complete shit. I said, "I said you sounded great," and she said "You did?" She literally had not even heard me say I thought she sounded great.

Here's another fact about the music world. People are often loath to tell you that you don't sound good (or don't sound great). Musicians know this, and so every time someone tells you that performance was great, there's a little part of you that wonders if you're being lied to. Often you'll get hired by a contractor to play a gig, and then never get called by them again. Sometimes that's because they have their regular people and you were just a stand in, or because they died or moved or whatever. Other times it's because they didn't like your playing. But they never tell you which one it is. So every time you don't get called back for a gig, regardless of what the actual reason is, there's a chance it's because you weren't good enough. Feedback is not consistent and it is not reliable.

So given those two facts, is it a wonder musicians can suffer from imposter syndrome? It's not a question of, "people will realize I can't play guitar," it's the very fine line between being very very good, and being great. Regardless of which side of the line you're on, you're always wondering.

Does that clear things up?