I think he’s saying that it’s dangerous to think that your messages are safe from being uploaded to other companies because even if your device protects you, the people that you message might be using devices that do not.
Ideally then you’d limit the amount of SMS messages you send at all, and use a secure messenger like Riot.im.
There is no such thing as 100% security and privacy but we should strive to achieve the best security and privacy that we can.
