Here he is asserting that one particular interpretation of the referendum result is an objective fact.
It's one thing to question an interviewee as a devil's advocate ("Some people say X..."), but he goes beyond that.
Compare that to his airbrushing of the prospect of the UK staying in the single market, which at least some MPs in the Commons support.
But, more fundamentally, there are other points that the interview should have focused on.
Here's a proper piece of journalism by @tconnellyRTE which analyses these issues:
Sadly, Humphrys' approach is too partisan, ignorant and irrelevant to cover Brexit effectively.