He was practically playing "run-run"! He didn't even leave the halflings at home at the beginning to level up the hero, even though his goal was simply to gather resources.

Thank you, Maestro!
So, the first mistake of the player: he was moving around with a hero-scout (i.e., the one who only explores the territory and gathers resources without engaging in battles) with slow units in his army. Let's try to calculate how much this inaccuracy cost him.
A hero with halflings has 11 movement points, and a hero with pigs has 14 movement points. Thus, in a week, a hero with halflings has 77 movement points, while a hero with pigs has 98!!, meaning he can move almost TWO DAYS more! This is the price of an inaccurate, template-based move!