I believe this photo has been taken using a very long exposure and a tripod.
I don't believe it has been Photoshop'd or HDR'rd as if you look closely you will see the ghost of a number of persons in the lower right corner. There is also no evidence of editing on the skyline around the antennae and the stars are slightly elongated.
In answer to the question about how to blend, it is a very simple technique.
Here is an unsharpened image I have done some years ago doing it with Photoshop as mentioned in another thread...
Cheers
J