Although this seems to be following too closely on the heels of the
"Is Tintin Christian?" thread, and therefore much of this sort of argument is thrashed out there, I can't see how the example you give in the body of your message ties in with your choice of subject title? Why does the fact that Haddock behaves badly in a Bhuddist monastery (and as mitsuhirato says, probably through ignorance) make him an atheist - he might just be a rude theist.
I've taken the step to change the title, broadening it out from "Haddock: An atheist?" to "Haddock: Is he religious?", so that it can look for ways in which his attitudes to religion can be discussed, rather than limiting it to a binary choice.