The fact that a cryptographer might scoff and laugh at the proposition doesn't mean that a normal programmer couldn't fall victim to that illusion?
In any case -- yes. Both things are likely and you made a strong point for the "malice" side.
Still, it makes me wonder why would Durov run from Russia if he was willing to backdoor Telegram? Why not remain in Russia and backdoor it while being there? Why the extra trouble? Or maybe he didn't want to backdoor it for Russia but for other nation(s)?