not sure what you mean, I use the official app on OSX and it has the secret chat option. click on a contact, it shows you all the infos including "start secret chat"
Anyone could claim absolutely anything, and the bigger the player the more likely it would be without any negative consequences (and with positive ones until the discovery - and sometimes even after), even if it's discovered to be an outright, blatant lie. Not like Telegram is unique or exceptional in this regard.