I am not sure you will be allowed to complete your landing. They will see you as non-essential travel.
Does "non essential" apply to air travel ? From what I have seen it's only for Land travelers. i.e. a Canadian or a PR can fly back to Canada from US (Fact) but they cannot drive to Canada from US because they would not be classed as essential.
I think same applies in this case the only thing I am not sure about is the self isolation part but I guess if you are not leaving the airport and are flying back the same day then maybe ok ?
He might however be subject to quarantine once he lands back in the US as he's coming back to stay.