After watchin' the clip a few more times, I've come to this idea of why Roberts is acting the way he is. Let's put this into thought; Maroni is a mobster, gang leader, crime boss. He's a bad dude who does bad things. Everyone 'knows' it, Loeb knows it and Engel knows it. He's asked to be on the news and what do you think he's suppose to act like? A bad ass? No, he's going to down play himself and act some what dumb to the questions and remarks being made to him. He's going to act as if he's just some average person who can't understand what money laundering is. So yeah, he's gonna seem like a dim-wit wiseass to make people think differently of him.
So perhaps he puts on an "act" when in public. Ya know what I'm sayin'?