I think he's saying more about all of LG's custom ROM features and (arguably) gimmicky features.
I'm no LG guy, but I've surely heard and read how shitty their software is, people hate it WAY more than touchwiz. I'm an HTC guy, and going from Sense to an AOSP rom, both based on the same version of Android, the battery life jump is HUGE. Manufacturer's roms burn more battery period. Bloatware burns more battery, gimmicky features burn more battery. The Nexus 5 will have none of these things, and the guy you are quoting is claiming these will make up for the 700mAh difference. I'm not sure I agree with him, but if you also factor in the larger screen, I'd bet it's pretty damn close when it comes to usable battery life.
One car has a 24 gallon tank and gets 15 miles per gallon.
One car has a 16 gallon tank and gets 23 miles per gallon.
Both make it about the same distance on one tank of gas.