Further tests [...] also came back negetive
Hopefully their lab testing is better than their spelling.
But seriously: This is just it. You cannot really assert that someone is clear of virus while under antiviral therapy. They may have a few thousand infected cells in a lymph node with moderately low activity (thanks to e.g. reverse transcriptase inhibition), but they're still there. Now, maybe there's a few hundred or so virusses total floating around in blood, but the chance of actually catching one in a 1-2 ml blood sample isn't so terribly high (and then, a single virus (or say half a dozen) in a blood sample may quite possibly be under detection threshold, even for PCR).
An undetectable viral load and complete eradication of the virus from the body are two very different things.