Setting aside the usual arguments on the anti- and pro-AI art debate and the nature of creativity itself, perhaps the negative reaction that the Redditor encountered is part of a sea change in opinion among many people that think corporate AI platforms are exploitive and extractive in nature because their datasets rely on copyrighted material without the original artists’ permission. And that’s without getting into AI’s negative drag on the environment.
That’s pretty reductive and bad comparison. Your example boils down to saying that you could argue guitarist is a machine assisted.