In all honesty, DO's need to get off their horse about osteopathy sometimes. Medicine is medicine. Just because you have one additional course dedicated to osteopathy doesn't acknowledge you as being
that different from MD schools.
I want to be a doctor should be all you should have to say for why you applied to both sides. If they want try and preach how different their school is you can counter-argue the point about how many people take the USMLE and go towards getting their residency from allo schools. But I'm not saying you should because the last thing you would want to do is piss off an interviewer.