Board Game Arena

In an otherwise fine tutorial, it wasn’t explained why the carpenter’s coins jumped from two coins to four coins. Originally, building the poulterer unlocked 2 gold to the carpenter. But then later in the tutorial, the carpenter’s gold jumped to four gold for no apparent reason. Was this an error in the tutorial or can someone explain the jump?

Looking at the rulebook, I realize now that another player must have played a villager that required a padlock payment of two gold to a carpenter, and I was the only player with a carpenter.