Specifically targeting a population, and the coincidental demographics of that population are two entirely different things.
That 70% is part of the 100% which they are actually targeting, but only coincidentally. There are plenty of fast food ads targeting health-conscious consumers.
You could also point out that 70% of Americans are also Christian, but that doesn't mean every company that sells to Americans specifically targets Christian customers...
...also, most large fast food companies also have a significant presence in multiple countries.
