Well average IQ of the human population around the world has been increasing in the past decades if not centuries. And it's not because we're evolving within a few generations.
Minor nitpick. I understand what you're saying but average IQ is by definition 100 (with a deviation of 15). The scale itself moves, e.g. new 100 would usually be more than 100 in previous iteration of the test [1]
Your parent is right: IQ has been increasing. Even in countries where you wouldn't expect the cause to be improved nutrition. But nobody really knows why, nor has anybody discovered an intervention that can, on its own, reliably increase IQ.
Not only nutrition, but overall childhood experience is getting better worldwide. Even in countries that had no malnutrition, there was a lot of space to improve in children<->parents relationships etc.
Meanwhile some countries that were really good in all areas a while ago are now reporting minor IQ decrease..
