Even before the trip to Durham, how is physically going back to work *after* learning that you are in a COVID+ household (to a degree of confidence where you were anticipating incapacitation) permitted?

"If your [COVID positive wife asks you to return to work while you fear for your ability to be healthy enough to look after your child in the subsequent 24 hours], you should say no."

At the point he returned to work, he was operating at this point under the assumption he was in the pre-symptomatic period. Noonish is about 0.7 days before his symptom onset the next morning. Infectiousness peaks on average... 0.7 days before symptoms. https://www.nature.com/articles/s41591-020-0869-5

It is certainly an evidence-based 'worst time to return to work'. In his defence, this paper was not officially published for another two weeks, although the idea of presymptomatic stage being particularly infectious one was not new.