Actually, the influenza virus is much less prevalent than we think. The actual influenza virus is very dangerous and can cause issues with the very young/old/pregnant,and that's what immunizations are targeted towards, back before immunizations, influenza was deadly and was a killer, the vaccinations help prevent this now, however it doesn't prevent us from getting one of the other hundreds of viruses, that mimick actual influenza. There is everything from the rhinovirus (cold) to Coronavirus in kids (GI typically) to the countless number of viral illnesses that simply make you feel like crap.
Working in a hospital/school and fields like that (I assume a locker room) obviously the chances of catching the are higher, and as north buffalo points out, hand washing and things similar are the #1 way of preventing spread.
As for the being called "the flu" I think that's just what society calls it now, patients that come in with bronchitis say they have the flu, even if the flu swab was negative, I don't expect the whole county to be docs or medically trained, but we have a legit education issue in the country when 90 percent of patients don't know the difference between a bacteria and a virus.
So yeah, flu sucks, if you get influenza A or B then you're in for a rough week, GI bug may be flu or may be one of countless other microbes, and most likely I expect teammates to catch it.