I'm surprised Tamura ended up cursed as well, I thought for sure this was meant to be a pretext for a frame-up.
I mean, there's a general perception of astrologers/astronomers being preoccupied with looking at the heavens and being oblivious to what's going on down on earth. I wouldn't rule out stargazing as a practice in this world, mystical or mundane.
Everything I found about "space case" as a colloquialism pointed to it coming about in the 20th century - namely,
after we started actually going up into space (or al least putting stuff up there, getting us up close and personal with The Vacuum).
Before that, I don't recall finding anything about astronomers
pre-19th century really knowing anything about what was going on Up/Out There, so the specific context of it being "space" and not just "the heavens" (as you yourself phrased it) isn't necessarily known. I did just find that Pascal hypothesized in the 1650s that, because atmospheric pressure decreased the higher in elevation you went (from sea level up on a mountain, in his experiment), that it might continue to do so until it reached 'actual zero pressure' around 89km or so. So there is technical precedent for knowing about the vacuum of space before we started sending up rockets to verify
But, given everything we've seen about this world, they don't appear to have reached "internal combustion", and even with magic they're using literal horse power. They're probably not sending Magic Sputnik up and through their version of the ozone layer to confirm anything.
That's not to say it couldn't be the case. But that's my rationale for why "airhead" works just fine and arguably better in the chapter in the context provided, if only in a pedantic sense.
