Yes, I’m afraid that you are still misunderstanding the research. Your linked article speaks about gene flow associated with the movement of pre-Proto-Germanic speakers to Scandinavia, but later Proto-Germanic formed in southern Scandinavia according to the longstanding consensus. This is clearly spelled out in the abstract: “Following the disintegration of Proto-Germanic, we find by 1650 BP a southward push from Southern Scandinavia.”

There’s no new theory here at all, just some nice archaeogenetic evidence to support a quite traditional view. FWIW, I work in a closely related field and am constantly reading Germanic–Finnic and Baltic–Finnic contact literature, and I can assure you this is old-hat stuff.

Do you think I'm misunderstanding something other than that I'm not drawing the same distinction between proto-Germanic and "paleo-Germanic" that that paper appeals to?

You've quoted something that says after proto-Germanic had diversified, daughter lineages left southern Scandinavia to establish themselves elsewhere in the world.

But I pointed out a completely different idea in the paper, that before proto-Germanic diversified, about 2000 years before the time you mention, its speakers arrived in Scandinavia from "the northeast coast of the Baltic".

Your post above wrote “the location of the proto-Germanic speakers”. Terminology matters; Proto-Germanic is something strictly defined as to what it was, with a longstanding consensus about where and when it was. If you wanted to talk about pre-Proto-Germanic speakers (or “Paleo-Germanic” speakers as this paper does, though I suspect some would quibble with that term used for a very early date), then you could have done so.

Moreover, you posted about a “new theory”, but the paper here only gives new evidence for an old theory.