> the flu was somehow eradicated at the outset of mass covid testing, many of the covid tests did not distinguish between the flu and covid.

What do you mean when you say that tests did not distinguish between COVID and the flu? Are you referring to simultaneous infection? I'm not aware of any PCR or antigen tests for COVID which would produce positive results for flu patients. Nor any antigen or rapid molecular assays for the flu which would produce positives for COVID patients.

Seems much more reasonable that social distancing and masking significantly reduced flu transmission.