They are probably just hoping that you will do the MPH program (more $$$ for them and less for you!).
Err... not really. When I was in Tufts MBS I was on the fence for a while about doing the MPH and ended up meeting with Dr. Schlaff, the MPH program director. He actually advised against me taking it there saying that I could take it later once I finish medical school if I still wanted to. At least during the first year of the MBS program there was absolutely zero pressure to do the MPH.