The affix ḍhinuk comes in the sense of 'enounced by him' after the word chagalina,
The word छगलिन् being a word denoting the pupil of कलापी would have taken णिनि 4.3.104. This debars that. Thus छागलेयिनः 'who study the Chhandas enounced by Chhagali'.,