I’m more inclined to thinking that he had a false-positive test, went hod-wild on Tx and got a valid negative test, but I don’t know.
It's possible he had a false positive, or that his most recent one was a false negative?
But testing positive for the virus, getting monoclonal antibodies, and then testing negative roughly a week later isn't entirely out of the realm of possibility.
He revealed the news on Wednesday that he had tested positive on Sunday the 29th. (after feeling bad the day before, the 28th)
It's also quite possible that he was vaccinated (he's been coy about revealing whether or not he was), and there have been studies showing that vaccinated people clear the virus faster than unvaccinated.
Monoclonal antibodies was the same treatment Trump (an old guy, who was overweight, and ate cheeseburgers all the time) received, and he was out of the hospital after 3 days, and tested negative at 10 days (as an unvaccinated elderly person at the time)
So Joe testing negative 5 days or so later (especially if he was vaccinated, and just didn't publicize it) after receiving a proven treatment, isn't out of the realm of possibility.