Yeah, that was a figure of speech. Encrypted email is probably still the most secure thing available to most people, even these days. That's because it as asynchronous and offline. You can do it in your air gapped system in your shielded and guarded basement if you really want to. That is as opposed to some instant messaging scheme running on an inherently insecure device like a smart phone where there is access to the messages all the time.

Delta Chat is an instant messaging scheme. It is still good to use preexisting standards where possible.