Real hogs don't follow the farmer. They are moved from one pen to the next by means of gates and chutes by getting behind and putting your heel in their backsides and stopping them going the way you don't want them to go by putting a boot heel in their snouts.

You can train them to follow food. In fact, that's how they get hogs to race. They put one oreo cookie in the slop trough at the end of the track. After the first time the hogs know its there and they also know that the first one there gets the cookie.

In game you can throw food and if the boar is hungry it will go toward the food. You can pick the food up and throw it farther and the boar will continue following until it gets the food.

Why would you expect in game boars to behave differently than real ones?