That is end to end from your phone to their phone, and they are talking about 3rd parties outside the app. As your physically typing the the information into the chat message box, and before you send it, the app itself should have access to the plain text coming from the keyboard, which it then encrypts before it leaves your phone.

Similarly it needs decrypted on the other side and displayed to the other user, at which time the app again has accesd to clear text versions.

I don't believe there's any way to encrypt the message before the app sends the message / while it is displaying to the recipient