Getting Litecoin cash out of my Trezor
LCC-core is not asking for your Trezor passphrase (25-word) which, as you said, you didn't set up.  LCC-core is asking for your wallet.dat passphrase which is the passphrase used to encrypt the contents of the LCC-core wallet.dat file.  This was a passphrase you set when you originally installed and set up the LCC-core software.

Just a point of advice.  You might be better served using the Electrum-LCC software since it can talk directly to Trezor.  No need to extract private keys (which is inherently risky)