One of them does rather dishonest marketing, the other is upfront about capabilities and defaults.

Telegram: we do E2E!* That makes us MORE SECURE than other messengers!

Matrix: you can enable E2E if you want.

* just not by default†

† unless you count "E2E" security between your client and our servers,‡ which we'll confusingly highlight in our security documentation as if it were special††

‡ you don't really need E2E anyway because we store your data in shell companies across the world

†† I guess it is "special" because Telegram invented its own crypto algorithms?

I'd like Telegram a lot more if they would stop with their bullshit claims, because it's actually a good service for some usecases. While reading the article I was hoping it was just written by a clueless Telegram fanboy, but reality is disappointing…