It's not the flu. It's not in the same virus family. However, at a low level its symptoms are similar (as are many many viruses).
However, a certain % of cases are more serious, and these cases have symptoms quite unlike even bad cases of the flu, mostly due to how it affects lung functioning.
So if you have a weak case like most healthy young and middle-aged people will, then you won't be able to tell the difference. But if you have a serious case it can look VERY different, and that switch can come quickly.