The "article" reads like a rant from a user who is upset, that a free app now includes a cryptocoin partnership...
A large part of the value proposition has been "combining identities, users can sign attestation and if you see one you know and can validate that the user proved this as part of their identity". I can see how someone would label a mechanism that causes the app to make such a claim without the user being part of it a a backdoor. (EDIT: per their comment, keybase claims that the user always has to agree to sign up for a wallet, so it'd just be about publicly linking it)