How was Trump “misled” about his authority to fire Comey?
He did fire Comey. And he clearly had the authority to fire him.
Those who follow these things know that it was completely within the purview of the President’s authority to fire the FBI Director for any reason he likes...he doesn’t need any Congressional approval to do it. (Getting a replacement is different, obviously)
He can fire someone even if he thinks he is simply not aggressive enough, no other “cause” is needed.
But that may not have been apparent to Trump who doesn’t have as much experience or exposure to this end of things, so he may have been getting advice.
It sounds like this Swamp Rat of a lawyer gave him deliberately crappy advice. I read his profile, and I don’t like it.