Depends on his location. All we get here are Carolina chickadees. Up in the mountains we'll start getting Black-Capped, and they hybridize where their ranges overlap.
I am located in Toronto, Canada. I think you are both right that it is a black-capped chickadee. Your suggestions steered me to this: http://www.allaboutbirds.org/guide/Black-capped_Chickadee/id
, which seems to confirm the probability.