This reminds me of when my first roommate in college seriously asked me why black people sing all the time.

You should just tell them, you're just saying hello. If anyone is over-thinking anything, THEY are. Who cares if you greet other black people. What's the big deal?
Originally Posted by midgi

+1 to the bolded. And if they persist in asking, dust off the phrase from the 90's - "It's a black thing, you wouldn't understand."