I could not find anything about google or other browser vendors in the article.

My take is that you should trust provider (developer, hoster) of said encryption app to send you actual implementation, not something that looks like the real deal, but does not encrypt anything. From a regular user's point of view: you can not inspect what you run (due to technical reasons, that on the web anything can be downloaded and executed at any moment, swapping implementation on the fly. And due to skills needed to actually read and understand executed scripts), so you can only believe and trust. At which point usual TLS is surely enough.