Influenza has a much lower transmission rate than covid19. Of course cases will greatly decline versus previous years with so many gatherings worldwide shut down. You can’t deny that big groups of people spread virus.
There are distinct tests for flu and covid19. It is very easy to figure out if a patient has one (or even both). In MOST cases.
Medicine is never 100%, mistakes happen and we can often find a few rare cases that contradict nearly anything we’ve learned. This does not mean we have a global conspiracy by nearly every medical professional on earth...
Kind of hard to imagine 9 nuns in one convent dying of flu.