Canny means clever in a shrewd and careful way that benefits oneself, or outwits someone else:
The canny fox had learnt to enter the chickens' pen through a hole unseen by the guard dog.
No. If you give a 'canny' answer, it means that you give a good, knowledgable answer. If you're canny, it means that you're either an expert on something, or that you're really good at something.
It probably means that the boy just said the first word that came to mind, but the actual definition is
a. Steady, restrained, and gentle.
b. Snug and quiet.