To be willing to claim lineage back to any historical figure means you stipulate that historical figure existed. If you are claiming you can trace back to David back to Adam means you accept the validity of the Old Testament (or however your belief calls it).
Personally, this is the first time I've ever heard Norse mythology being tied into the ancient Hebrew text. I've heard a lot but clearly not everything, and I have no interest in all of the crazy. I'm tired of dealing with all of the crazy I've had to deal with up to now
The writers of those genealogies indeed claimed that the god Odin did exist as a real historical person. But that doesn't mean that we have to accept their claim.
Similarly, anyone claiming descent from King David is indeed claiming that the he was a real historical figure, but we don't need to accept their claim.
As for tracing Odin's lineage back to the Hebrew patriarchs, that is of course a form of syncretism, where people who believe in multiple religions create a mix of them for various purposes.