Yup, what is meant by infection waste? HIV, Hepatitis? what kind of dirty bombs could they make with that kind of filth?
Hard to say. HIV and Hepatitis aren't spread simply by airborne germs - they have to get directly into the blood stream. And plenty of "infectious" categorized medical waste is really "potentially infectious." They don't know that it contains disease-causing microbes; they're just being careful.
I suspect these guys were just being greedy. There's money to be made in waste disposal, and of course you pocket more profits if you don't bother to correctly dispose!