I assume they are talking about E2E-encryption, since that would prevent them from spying on their users even if they wanted to (assuming the client doesn't leak the key).
That said, E2E-encryption doesn't come without drawbacks, for example you would lose all your messages if you lost access to your device and any backup mechanism.
That said, E2E-encryption doesn't come without drawbacks, for example you would lose all your messages if you lost access to your device and any backup mechanism.