i'm still not seeing your point. i'm sorry, i'm honestly confused. look at his screenshot, he does not have food to feed anybody else. he has health room for 14 more people but that spare health is doing him no good because he cannot get that extra food to turn it into population is what i mean.
The spare health that he has is irrelevant. He could have 4800 population instead of 48 population and he would still have 14 pollution.
What is relevant is that each person is costing him 2 food.
If he had to worry about people producing pollution, each of the first 14 people (assuming he has no coal) would cost 2 food, but each person after the first 14 costs 3 food. That's because he breaks even on

vs.

at 14 people.
Since he has 48 food available, the first 14 people would cost him 28 food. He'll have 20 food left. That remaining 20 food can only support 6 people since these people consume 3 food each. That's a total of 20 "normal" people in the city.
If he has access to Coal, I believe he'll only get 19 people since I believe Coal produces 4

on its own. If Coal produces 2

on its own, then he'll still be able to support all 20 people that he can without.
With the National Park, he can support all 24 people that he (obviously) has in his city. He also gets an additional 7 free specialists which brings him to a total of 31 real population (rather than his listed 24).
I'm not saying that he could support even more people than he has now. He obviously doesn't have enough food for that. What I'm saying is that he can support a lot more people now (his total of 31 real population) than he could support if he did not have the National Park.
With National Park (see screenshot): 24 "normal" people + 7 free = 31 total.
Without Nat. Park: 20 total people.