It's best practice to use "coronavirus" for coronaviruses, and "flu" for influenza.

While they can cause similar symptoms, they are very different diseases, caused by viruses that have no particular genetic link.

It's absolutely not appropriate to call these "flu". That is a contraction of "influenza", which is an entirely different family of viruses.

And yes, the family is named "coronavirus". The one we're dealing with now is a strain properly calls SARS-Cov-2, which causes a disease officially termed COVID-19.

Well, it's not influenza...

Flu viruses are usually described more specifically too: H1N5 and the like

Where do people get this? Covid is nothing to do with influenza. Some of the viruses which cause the ‘common cold’ are coronaviruses, but flu is unrelated.