these optimization were done under Google's leadership. N5 is using stock android without much optimizations as it is suppose to act more like a developer device. Another point: Moto X doesn't have heating problem as other flagships (not as severe as others). The 2 Krait 300 are allowed to run at full clockspeed for longer without throttling something i doubt Nexus 5 can.
That article doesn't list Nexus 5, also we are talking about Moto X 2014, which will have Krait 400, quad core, just like N5 but faster hence producing more heat. The entire Snapdragon 8xx line up suffers from Heating issues.
Also from the article you referenced, battery is on par, nothing spectacular: AnandTech | Moto X Review
Snapdragon 8xx eats through battery, there is a limit to how much you can optimize it, so I'll believe it when I see it.