Is this article sponsored? Hard to say if it's without such label, but easy to say when it recommends close-source apps, or when server is close-source and network owned by social network...
It also misses community-based projects like Tox, Ring that are end-to-end encrypted and decentralized (DHT) by design and Riot (federalised Slack-like with end-to-end encryption), or Wire - one of the most feature-complete IMs.