After the verb vad , preceded by anu when it is intransitively used, the ātmanepada is used, when the sense is that of 'speaking articulately in a similar manner'.,
As अनुवदते कठः कलापस्य katha is echoing or imitates kalapa. He reutters exactly what the kalapa-reader or the teacher says. The word anu here means similarly.
Why do we say 'in the Intransitive'? Because when it is used in the transitive it takes the affixes of the Parasmaipada. As पूर्वमेव यजुरुदितमनुवदति, 'he repeats the yajurveda which he had learned before.'
The words 'uttering of articulate speech' are understood here also. Otherwise अनुवदति वीणा 'the lute resounds,' here it is Parasmaipada.,