As I understand it, the medical doesn't HAVE TO be completed before the interview. Because there were cases when someone couldn't get the medical done in time and they asked what they should do about the interview. And they were told to go to the interview anyway, instead of rescheduling it. You just won't get your visa until the medical is completed. And it takes them approx. 5 days to send the medical results to the consulate, that's why they say it should be completed at least 5 days before, to not delay your visa.
But happy to be corrected.