Big (1988)

Billy: Here, take this. [Hands Josh a handful of money.]
Josh: Billy, where did you get this?
Billy: From my dad's top drawer.
Josh: You stole money from your father?
Billy: It's his emergency money.
Josh: Jesus, Billy.
Billy: Well what do you call this?

Trivia: The big piano scene was actually rehearsed months before shooting. Tom and Robert had to practise on a cardboard cut out with exact dimensions of the real piano. On the day of shooting there were stunt doubles instead of them to film their feet. But once the director saw that they could do it, the stunt doubles were never used.

Question: When Josh is giving his presentation to everybody, why did Paul say he doesn't get it? Was he mocking Josh? If so, why?