A 2012 article by Vincent Tournier on the Mahavastu and its place regarding the Vinaya Pitaka. It argues that the Mahavastu is indeed a Vinaya text (as it is classified in SuttaCentral).
Vinaya has always included extensive narrative and mythology, and the Mahavastu extends that, adding copious legends and fables to the extent that some scholars have doubted that it is a Vinaya text at all. But the manuscript explicitly identifies itself as Vinaya.
2012a_The_Mahavastu_and_the_Vinayapiak.pdf (312.8 KB)