every part of that tweet is false, from the claim there were no flu cases to the claim that governments across the world all use the same test. it's all crap.
the test in reference wasn't supposed to test for flu at all, but the CDC wanted paganizations to use tests that could identify both viruses. The test cant even falsely identify flu as covid because the PCR primers wouldn't work on any component of the influenza genome. you can see the primers here:
https://www.cdc.gov/coronavirus/2019-ncov/lab/rt-pcr-panel-primer-probes.html 
