«وَالْأَمْرُ الثَّانِي: أَنَّ الرَّاوِيَ قَدْ يَكُونُ مُقِلًّا مِنَ الْحَدِيثِ»
The second cause is that a transmitter may narrate very little hadith.
When only one pupil is known to transmit from a person, the range of available information may be restricted. Scholars devoted a category, al-wuḥdān, to such narrators.
Having one known student is not the same as being weak. Limited transmission can make critical information scarce, but any judgment of acceptance or rejection requires examination of relevant evidence and evaluations. Wuḥdān is an important classificatory description, not a self-sufficient verdict of discredit.