A wallet.dat file contains no information specific to a particular install of Bitcoin Core, or its configured data and wallet directories.
You can freely copy just the wallet file to another instance, without having to copy the block data or other information such as peers, mempool, etc.
It is possible to have a nine word mnemonic + 1 passphrase word, although it is unusual - you'd probably remember if you specifically chose that combination.
Electrum in BIP39 mode should be able to work with it.
It could also be some random wallet's passphrase system which does not conform to BIP39, in which case electrum will give you a checksum error ...