I read in The Collegeville Bible Commentary: Old Testament "Genesis" by Diane Bergant that the similar names in both Cainite and Sethite genealogies found in Genesis 4 and 5 such as Lamech, Enoch, Methushael/Methuselah, and Mehuyael/Mahalael are a result of a single account being edited by both "Yahwist" and "Priestly" sources of the Documentary Hypothesis. (The DH postulates multiple editors of the text that became the torah.) The names Irad and Jared are also very similar.
Bergant writes (page 46):
There are points of conflict between this genealogy (Genesis 4) and the Priestly genealogy in Genesis 5. Some of the Names are repeated (Enoch,Lamech), and some the names are simply variations of names in the Yahwist genealogy (Mehujael/Mahalalel) and (Methusael/Methuselah). It appears that both genealogies come from a common source that has undergone a long period of transmission.
How does the Jewish tradition understand the strong parallels between these genealogies?