Potter is an innocent and humble adult who just really cares about his son, Pup, and his pottery. All of his pottery was destroyed due to BK's actions and his son was sent into a hot air balloon, all by himself, adrift amongst the winds. Despite all that BK has done, he doesn't get angry with him, but more upset that his son is missing. 

I imagine Potter sounding like a stern adult with a lot of worry and anxiety over the fact that all his favorite pottery and his son are now either smashed or missing. He doesn't seem to get mad, he just seems to get upset at himself. There are a lot of places you can go with this character, so feel free to experiment with what is given!