Further to the idea it's an AU:
The air raid warden in the ep:
An air raid warden from our time:
There seems to be a difference...
(off to Google)
Both St Paul's and Buck Pal
were bombed. The Chapel at the Palace was destroyed but the rest was minor damage. St Paul's was also hit by bombs, but the damage was minor or they didn't explode. The implication was it was the same night, but I can't find anything that said they were bombed together.
Here's what I think. The Moff plants tiny clues (like the above) as well as a couple of big obvious ones (Amy's memory re Daleks) to indicate we're not in Kansas anymore. Just watch carefully and you'll pick things up. For example next week, is River Song...
our River Song?