I expect it's redrawn from photos, same with stuff like the station. From what I gather it's not uncommon for background elements to be copied in manga, and of course doujins being fan work they've got even more leeway. But agreed that overall the art is really good.
The redrawn artwork is really good? But, by the time it has been published, it is no longer redrawn. Or a drawing of an animal.
Well, given how it's actually pretty tough to make a trace look good (look at how bad Greg Land's stuff for Marvel can be at times). I'd give a lot of credit to the inks on that score, they're pretty good, and they're quite good on the (obviously non-traced) character stuff.
