The angles are about right but there are a few discrepancies that also lead me to suspect it might be 'shopped.
It is a long exposure as evidenced by the smooth look of the water.
My thought is that the star filled sky has been added. In part because of the long exposure there is no "trailing" of the stars.
The falls light up like that under particular conditions when the setting sun lights up the water. The suns angle hits it the same for about 2 weeks in February and October but in October the falls are almost always dry so no firefall effect.
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If it only occurs during sunset, then it's a definite shop; the light from the sun would have over-exposed the sky. That kind of exposure can only be made long after sunset.The star trails effect itself depends on a few factors, though. The trails are much less noticeable at wide angles, for instance. Using a high ISO to minimize the exposure time can help as well, but as you noted the smoothness of the water kind of rules that out.
My guess is it's a composite of three different shots: one taken at sunset to get the falls, then two well after sunset, with one at high ISO to get the stars, and one with a lower ISO and much longer exposure to get the water.
ETA: I went and read the description the site. This effect was supposed to have been caused by the setting moon, so it could very well be one photograph, depending on the quality of the camera. Or it could have been an HDR shot. Either way, there was some heavy editing involved. There are a few areas around the edge of the mountain that appear to be lighter than they should be, which is a symptom of either HDR or abusing the lift shadows (IIRC) slider in Photoshop.
