www.jtosti.com/noms has something to say about Carrillo (in French, unfortunately). Tosti accepts that the name means "cheek", and suggests that it is a nickname for a glutton. He adds the cautionary note that we cannot know the mediaeval mindset that produced such a nickname. For myself I don't think we should too hastily dismiss a connection between carrillo and carro, carreta, etc. It's possible that this is a metonym for someone who drove or built carts.