No, its because these people are not being tested for flu. They’re being tested for Covid.
632,000 flu tests have been conducted this flu season. Only 1,387 have been positive. Influenza virus is not remotely related to SARS-CoV-2 (they're as similar as human beings and snails), and the testing is highly specific to each one.
So people ARE being tested for flu, they just aren't coming up positive. The people who are being tested for SARS-CoV-2 definitely have SARS-CoV-2 present at the point of collection (typically inside the nasal cavity) since the RT-PCR test used for laboratory confirmation triggers on the specific genetic sequences that distinguish SARS-CoV-2 from every other virus.