A nice find, but given that the rotation is minor along with it being THE key date coin, I don't think it's going to add any value.
Delusion, lol. That actually made me laugh. Illusion, my friend, optical illusion, and it most certainly is not.
Oh, forgot to look at the date...J/K. I love this coin, wish is was in the holder a little straighter though. C'mon, it's gotta make it a little exotic.
The coin is simply rotated in the holder which makes the reverse appear to be more rotated then allowable mint tolerances so yes, optical delusion.
I think it's rotated about 20 degrees, even accounting for the slight 5 degree rotation in the holder. I think 15 degrees is within tolerance for the mint, but up to 30 degree rotation on those dimes is commonplace. Many purists want pristine examples of the coins they collect, especially key dates. Thus, some would see this rotation as an imperfection, even thought it might be rarer than it not having that rotation. OTOH, if it was rotated 90 degrees or more, you'd have a highly desirable coin. There are no known 16-D's rotated at least 90 degrees, according to the rotated die census.