Most people have only heard of the lunar dynasty king Yayati, who was cursed with old age by Sukracharya (guru of the Asuras) and temporarily regained his youth by giving his old age to his youngest son Puru. Puru, along with Yayati's eldest son Yadu, started two of the most famous royal families, the Pauravas (which include both the Pandavas and Kauravas) and the Yadavas (which include Krishna). Less famous, however, is Yayati's father Nahusha. As I discuss in this question, Nahusha was such a good king on Earth that when Indra temporarily abandoned his post, the gods chose Nahusha to serve as the new king of the three worlds. But Nahusha was soon corrupted by his power, so the sage Agastya cursed him to become a large snake. Nahusha was only freed from the curse when he had a conversation with the Pandava Yudishthira about the proper way he should have lived his life, as described in the Vana Parva of the Mahabharata.
In any case, before he got corrupted, Nahusha was such a religious person that he was able to engage in Tapasya (deep meditation) and get Vedic verses directly from the gods. As you can see in the Rig Veda Anukramani compiled in my answer here, Nahusha was the one who heard verses 7-9 of Rig Veda Book 9 Hymn 101 (which you can read here) from the gods.
But my question is, why is Nahusha listed as "Nahusha Manava"? The term "Manava" is nowadays used to mean human, but here it's being used as a patronymic, i.e. it means "patrilineal descendant of Manu". But the thing is, as far as I can tell Nahusha wasn't a patrilineal descendant of Manu. Nahusha was the son of the king Ayu, who was the son of the king Puruavas. Puruavas' parents were Budha, god of the planet Mercury and son of Chandra the moon god, and Ila. Now Ila was an individual who kept changing between being a man and being a woman, but either way Ila was the child of Vaivasvata Manu.
So why would Nahusha have the patronymic Manava, if only his paternal grandmother was a descendant of Vaivasvata Manu? Shouldn't Nahusha's patronymic be related to his patrilineal ancestors like Ayu, Budha, Chandra, and Chandra's father Atri? The only source I found which addresses Nahusha's patronymic is this book, which says "Nahusha is said to be the son of the King Manu Samvarana".
So is this Manu Samvarana? Is he different from Vaivasvata Manu? Is it another name for the king Ayu?