I know the at home test are an average of metabolites and the test they used may have only measured the active THC level.
Thats incorrect. THC is present in the urine as a metabolite. ALL urine testing methodologies recognize metabolites only and not active THC.

Theres two possible reasons for your particular situation:

- Fluids were consumed prior to taking the home tests. Fluid consumption dilutes the THCA concentration to where a urine sample can test negative on an assay. The dilution phenomena is only temporary - once the fluids ingested had all been urinated out, the bladder is replensished with fresh THCA-laden urine and thus the donor is back to square one.

- misinterpretation of the home test results.