He's right. I dont know about the Russian influence part, but it isn't "fully safe". For anything people use it for, it's not even end to end encrypted, and they've given data to feds including German while claim to have never. Safe to assume the feds would wedge their way in.
If you wanted something secure, don't just take the word. Signal, Matrix, XMPP+OMEMO, Threema, Wire, all work great and they can't access your messages.