I think he understands that but when you have a situation where the real economy is growing only around 1% per year but rich people grow their wealth somewhere around 4-10% that can only come at someone else's expense.

In other words while the real economy might be growing as a "non-zero sum game" the growth of the elite and the rich far exceeds that and outpaces it. Net effect is that their wealth is wealth away from everyone else.