فَإِذَا كَانَ الْأَغْلَبُ مِنْ حَدِيثِهِ كَذَلِكَ كَانَ مَهْجُورَ الْحَدِيثِ غَيْرَ مَقْبُولِهِ وَلَا مُسْتَعْمَلِهِ
Translation: When this characterizes most of the person’s transmission, his reports are abandoned and not relied upon.
“The greater part” is decisive. An occasional problematic report from a generally precise narrator is not the same as a predominantly unreliable output. Al-Nawawī also notes that “munkar” can sometimes be used more broadly for an isolated report even from a precise trustworthy narrator; Muslim’s immediate discussion concerns objectionable and rejected munkar.