There are a variety of respiratory viruses that cause essentially the same upper respiratory symptoms. This includes other strains of coronavirus but most commonly it's rhinovirus or others. You can't really tell them apart without viral PCR test.
Is it possible that there was a different strain of coronavirus that was non lethal circulating in the US this winter? I got quite sick in December 2019 and the main symptom was sore throat/persistent cough. Many people in the community were sick as well. It was definitely not flu, I did get screened and was negative and I also get flu vaccination annually. Also the period of fever was short and not particularly high.