A subjectivist judges sound quality based on their personal preferences. The same way someone would judge food or art. If one finds the sound to their liking and then declares that to be good that is subjectivism.
An objectivist judges sound quality on accuracy to some reference. Maybe the recording or maybe live sound.
So we had people like Harry Pearson who cared nothing about measurements or science but was an objectivist because he felt there was an objective reference, “the absolute sound” the sound of live acoustic music, against which the accuracy of audio playback could be judged.
Then you have people like Floyd Toole and Sean Olive who strictly evaluated sound quality in their research using proper time synchronized quick switching double blind tests but are subjectivists. All of their studies were based on listener preferences. All scoring of their tests were done with subjective ratings.
And yet many would label Harry Pearson as the poster child for subjectivism in audio and would consider Toole and Olive to be poster children for objectivism in audio.