Yes, this is true. Hint: It is one of the recipes in my post above. it is one of the ones with an asterisk. Just remember, you have to let the villager complete what the stew makes him start to do. After he completes this activity which may take a minute or two, he will either shake his head (no building skill gained) or you will get the message this villager increased his building skill. As long as you keep the stew pot full, bored or hungry villagers will visit it!