There are 3 schools you need to be clear with their process and make some judgement. NW, CWRU and Boston.
NW and CWRU, clearly communicate to applicants after the interview decision for BS/MD program if they are not invited, applicant must reach out to UG to indicate that they are interested to be considered for UG. In Boston, you will NOT get any notification since their process informs upfront that you application will be considered only for the program you have applied like BS/MD program. So applicant need to call BU UG office and inform verbally that you want to be considered for UG and then they will change the status and the portal will reflect. Chances are some times students forget, wish BU also does send email like NW and CWRU to remind.
Now the unknown part, more from here say. Some of these schools think the pre-interview rejected students are possible candidates for other BS/MD programs and their yield will go down if offered UG admission. There is no factual evidence. But personally disagree if these school look that way. There is nothing wrong for students to get UG admission to pursue pre-med. My D rejected for NW UG and wait listed for CWRU and BU yet to be known. But life goes on.
FYI. Remember 1 parent told they made a decision not to apply to BU BS/MD for this reason and since his child was very keen on BU to join UG in case if he did not get any BS/MD program. His child had a very good record and went for interview to Miami HPME and Drexel, TCNJ/NJMS etc but still opted not to apply to BU BS/MD.