Pliny didn't quite make that report -- the "two" shows up later, part of a chain of cracked.com getting hold of "history" which Pliny himself only reports as a tidbit/piece of gossip passed on from elsewhere. Here is a link to a discussion on the same topic from years ago, and I'm sure there are others, although that doesn't mean that no one will have anything else new to add!

Pliny very clearly, from context, is saying that these Indians were supposed to have made the northeastern passage, going east around Asia, north around Siberia, and then through the North Sea to end up in Germany, not going around Africa, and the claim is indeed that they are genuine Indians as opposed to native Americans (another misleading part of the old Cracked chain).

For what it's worth, Pliny includes this story (and doesn't make a personal claim for its veracity -- he just passes on the story from Nepos) precisely because it seems incredible; he has a few stories of reported southern passages, and then tosses in that there's even this one odd story of a northern passage with Indians accidentally ending up among the Suebi. With how loose the story is, it's impossible to say exactly who they were, since even Pliny doesn't come across as very sure the story even happened.

Roman geographers at least had a solid idea of where India was, but the extent of Asia (and the horrid conditions that would entail for a passage around Russia) wasn't clear to them.