Ok. I have more details and clarification. It looks like I do have an air gap behind that OSB. After I drilled a hole to peek behind, I saw gypsum board and I assumed that I was looking at my neighbor's wall, but it is only about 2" from the OSB and the width of the studs are 3.5" so now I don't think it can be the wall. Also, the studs on my side does not protrude out behind the OSB into the air gap. So this is a mystery to me why I am seeing gypsum board behind there and not OSB even with a 2" air gap.
I guess my question is that with 3 air cavities, wouldn't my townhouse wall and most townhouse walls be a considered having a quadruple leaf effect?