They played a hunch and lost. The linked post details lots of mistakes, but this particular one doesn't seem like one to me.
You've got a business when people repeatedly exchange value with you. Kind words are validation of a sort, but the weakest kind. To go from there to spending a year building a platform is basically hearing what you want to hear. Better not to ask than to believe what you hear uncritically; if you don't ask, at least you know you don't know.
The data that was lost right here: "After that moment we basically stopped talking to artists for a year [...]"
Find customers as early as possible, engage with them as often as possible, and really really listen to what's being said. This is a huge benefit of bootstrapping. Customer engagement from the earliest possible time is vital to the process of transforming an idea into a product.
These are money-losing businesses. As we speak.
Real life is much more complicated.