I didn't read that - are you sure about this? I am reading that backdoors are being asked to be created on WhatsApp. Anyway the messages aren't stored.

From the article:

Priti Patel, the U.K.’s home secretary, has previously warned that Facebook’s plan to enable users to send end-to-end encrypted messages would benefit criminals, and called on social media firms to develop “back doors” to give intelligence agencies access to their messaging platforms.