It didn't surprise me at all. I doubt MH has been sat at home worried about his future. He would have been assured of a lucrative future role for going quietly when he did.
The whole thing was a setup and he was probably in on it. Convenient for him to let go of the reins after an exhausting 18 months (I am not his fan, but he did put in long hours and it must have been stressful) and then swan off with his new GF just as Boris wanted a change of tone and pace in the pandemic messaging.
It's MH's wife I feel sorry for. Hope she is glad to be rid of him and is doing OK.