The OG of the grain is showing you how much specific gravity that amount of grain is contributing in the recipe. As you scale the total recipe OG up, the grains OG will also scale equally since it's a keeping the grain weight % constant.

If you have a recipe set up using 1.050 OG with ten lbs of grain, let's say 80% 2 row and 20% flaked wheat then scale to use twice as much grain the OG of the 2 row will go from 40 to 80.* The PPG will remain at the expected ~36-37.

*But that's not really what's going to happen due to diminishing efficiency as OG increases).

It's basically equivalent to tracking percent of OG instead of % of total grain bill..

Don't confuse it with the grains PPG.