And I was actually standing up for them at that point and saying we can't say they infected anyone
Correct - we can't say they infected anyone.
That's not the point though.
The point is that we were asked to stay at home - and not to travel. One of the reasons was that you could get ill elsewhere, go to hospital and infect other people.
They went elsewhere. The son got ill (not Covid) and people who could have been infected went to Durham hospital.
Luckily the son was negative. It's unclear about his wife - the timeline looks interesting.
But the point is that 2 people, who were self isolating with someone with Covid 19, went to a hospital that was not their local London one.