typical vs. not atypical

I know that saying something is "not atypical" essentially means that it is indeed typical. However, is it grammatically incorrect to use the expression "not atypical"? Is there a slight variation in context between saying something is typical vs. not atypical? For example, let's say someone doesn't think the neighbor Bob walks his dog enough. You could either say "it is typical that Bob walks his dog". Or you could say "it's not atypical that Bob would walk his dog". The first may sound a little defensive. The second sounds supportive of Bob, but not as defensive?