The original could not detect, so therefore differentiation is a moot point.
Also, the test for flu was a separate test. So it would have had no effect on the lower flu incidence assuming we didn't test for flu at a lesser rate.
Do we have any numbers on this? I would imagine a lot of people who went to the doctor or whoever complaining of flu like symptoms would have been tested for covid.
In 2020-21 there were 1.11M flu tests over 33 weeks.
Results: Essentially a 0% positive test rate vs a peak of over 25%. A peak of about 125 cases vs 20,000 cases.
1: https://stacks.cdc.gov/view/cdc/54973 2: https://www.cdc.gov/flu/weekly/weeklyarchives2020-2021/data/...