Quote from: random_australian on Today at 04:43:46 AM

I opened bitcoin core with no wallet.dat, so it generated a new, empty one, with no bitcoin or transactions.

How exactly did you do this? Did you shutdown Bitcoin Core, move (not copy) the original wallet.dat file, and then start Bitcoin Core?

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Does bitcoin core store the private keys somewhere other than wallet.dat, or when a new wallet.dat is created on the same computer, is it deterministically linked to previous wallet.dat's created on that computer?

No.

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In short, how did my existing wallet.dat get the private key I imported when running a different, brand new, never before used wallet.dat?

It would appear that you've either imported that private key before... or you hadn't actually opened Bitcoin Core with a "new" wallet.dat and you imported it into your "original" wallet.dat