It’s definitely an added word by the owner of the seed phrase, right now you need to find how to gets those words and since you said some words are not familiar they might not be from BIP39 seed phrase. You can check the list here, maybe you can filter those words out that are not here. Then you might be facing a problem of whether the wallet is passphrase or not which is another problem aside the right arrangement of the words if gotten (although can be solved by bitarecover tool).