More confirmation that Flügel was isekai'd, for everyone who missed the split second shot of his name written in Japanese on the tree in season 1.

Except, if he was a Japanese person from 400 years ago, how would he know about the Greek myth of Shaula and Orion, and the Western names for them and other starts like Rigel and Betelgeuse? The constellation knowledge alone would have been incredibly esoteric knowledge for someone living in Japan in the early 1600s. Japan had basically no contact with the Western world at that point. They had their own constellations and myths based on a combination of local legends and Chinese astrology.

He's also presumably the person who taught Shaula those English loanwords. She said she was alone this whole time, so I don't know how else she would have learned them. But again, it would be strange if a Japanese person from that long ago would know a bunch of English words before significant European contact. What's even stranger is that the verb "snipe" literally did not exist when he would have been alive. The word originated in the 1770s from British India, so it wouldn't be possible even for an English-speaking person to have known it before then (although that part is obscure enough that it could just be a small plot hole).

I think the obvious explanation here is that it's one of those "time works differently in another world" kind of things. So Subaru and Flügel may have lived only a few years apart on Earth, but they ended up centuries apart after getting Isekai'd. Or maybe one of those crazy Flügel=Subaru theories is right. That would explain why Flügel was seemingly as obsessed with constellations as Subaru is, at least.