No, the world population is not considered by the time Satoshi created bitcoins because why would he only create 21 millions of it? When the number of population is much higher than that.
Many possible explanations for that but only satoshi knows.
In email to Mike Hearn, it's what satoshi wrote and you are free to interpret it but it can be a full explanation or just a partial one. Who knows?
My choice for the number of coins and distribution schedule was an educated guess. It was a difficult choice, because once the network is going it's locked in and we're stuck with it. I wanted to pick something that would make prices similar to existing currencies, but without knowing the future, that's very hard. I ended up picking something in the middle. If Bitcoin remains a small niche, it'll be worth less per unit than existing currencies. If you imagine it being used for some fraction of world commerce, then there's only going to be 21 million coins for the whole world, so it would be worth much more per unit. Values are 64-bit integers with 8 decimal places, so 1 coin is represented internally as 100000000. There's plenty of granularity if typical prices become small. For example, if 0.001 is worth 1 Euro, then it might be easier to change where the decimal point is displayed, so if you had 1 Bitcoin it's now displayed as 1000, and 0.001 is displayed as 1.
Anyway, it was set and can not be changed. I don't think of reasons to waste our time to figure out why it was set like that.
Furthermore, having more Bitcoin in total supply is not good for its value. Having less Bitcoin in total supply will make no sense because it will result in non-timing scarcity when the adoption for Bitcoin is not big enough. I think satoshi just did a magical timing set-up for Bitcoin total supply.