The identification is old and attractive, because the tortoise is a creation figure elsewhere in the same literature and a progenitor who is also a tortoise would join two strands neatly. The two may equally be homonyms, and a resemblance that suits a later theology is the kind of thing a later theology can produce.
What would resolve this Comparative evidence from cognate Indo-Iranian vocabulary, or a demonstration that the tortoise sense is attested for the name before the Prajapati tortoise material that makes it attractive.
OpenSanskrit etymology and comparative Indo-Iranian linguisticsArthur Anthony Macdonell, Vedic Mythology