I would not have answered. Especially not at 8am! WTF? 
I have no idea why some people on mumsnet, get so uppity and sniffy about people saying they don't like answering the door.
If I am not expecting anyone, and am not expecting a delivery, I don't usually answer. Why would I? 
Also, I can see who is at my door without them seeing me, so if it's someone I like/want to answer to, I answer. If it's a stranger (or someone I am not too keen on,) then I don't answer.
It's not LAW that you have to answer the door when you're not expecting someone. People shouldn't be made to feel bad, or like they're 'weirdos' if they don't want to answer the door.
In fact it's a bit of a weirdo (IMO) who goes to someone's house (uninvited) and expects to be let in. What if the person is asleep, or resting, or busy, or working, or just about to go out, or expecting someone, or their baby has just gone to sleep?
It's so rude and obnoxious and presumptuous to assume you can just knock on someone's door and be let in, and that the person you're visiting has nothing better to do than entertain you.
The posters on here, who think 'just popping in' is OK, (and anyone they visit absolutely should let them in, and entertain them,) are clearly the ones who are the dreaded popper-inners! 
And as for being 'open-mouthed with shock,' at some people not wanting to answer the door if they are not expecting someone. LMFAO.
As I said, some people are easily shocked!!!