I think your friend may be right, I used to see a painting very similar back in the 1960's. It may have hung in the Douglas Arms in Bethesda and I remember speaking to the owner of the painting. That one was titled with Ogwen Falls in it, though if you google paintings titled Ogwen Falls a more dramatic scene of the outfall of Llyn Ogwen seems to come up. I am sure the landlord of the Dougy name was Geoff, as his neice is the daughter of a neighbouring farmer I grew up with.
He was convinced that the artist had taken a bit of artistic license with the perspective and the actual rocks of the falls, because there is a very similar river scene an Ogwen bank just downstream from Tyn y Maes, though in the 20th century it would have been overpowered by the tips from the Penryn Quarries and the large rock on the left would be out of place. Unless that was altered with development of the A5 by Thomas Telford.
Can't help any more as I cannot remember the name of the artist, but if it was a scene that this particular artist painted many times it may well account for his skill in taking a bit of liberty with foreground and background.