This is true, your math is right, but assumes you allow the losing trades to go to expiry, and settle at 0. The best practice for Nadex is the same as non-binary trading: limit your losses. If the trade is going south on you and you apply a rule that you close it when it hits -$30 or -$40, then you lose $810-1,080 in your calculation. The profit on the 100 trades becomes $380-650. I almost always close my Nadex trades before expiry, win or lose, but that's just the way I trade it. Everyone has their own style.
I'm not defending the guy, just saying a 73% win rate is very good on any trading platform if you manage your risk.
Btw, from what I saw on the videos, Neal usually gets in for a $25-33 profit, so his average trade would have a slightly bigger return and smaller loss at expiry.