I thought that seed was only a mnemonic phrase for backup. Yes it is a backup but I didn't know that it was the private key. Hahahaha its been a long time since I used an offline wallet.
It is not technically a private key, but it's the source of the private keys, that if it's compromized, all private keys can be derived from it that are in that wallet.
So yes it's the source entropy of the private keys in that wallet ,and it's confidential.