It’s hard to imagine a time when the average Swede was only tft, 5”. Who did they “comingle” with to become as tall as they usually are today? Perhaps it was the Danes.
The Danes and the Watusi have historically been among the tallest of all.
It might be improved nutrtion. I just read somewhere else that people living in what is now North Korea used to be taller then those to their south. But now, after a few generations of communism, South Koreans are on average about 6” taller than North Koreans. Genetics wouldn’t have significantly changed in this length of time.
An improved diet as Europeans explored the world and brought new foods to market was an important factor in making them (all Europeans) taller, stronger, and healthier.
Coloradan beat me to it, but improved nutrition is the answer. Medieval nobles were often relative giants because of generations of access to more, richer, food (and intermarrying with mates of similar class).