The picture as described on the web site is a 'cone shaped cloud' looming above a hill, but doesn't say it is a twister, which I interpret as a tornado.
I still don't think the structure of the cloud is showing what most of us in the lower part of North America would associate with a tornado. This could be a lenticular cloud type, or other such cloud formation, but to me, at least, it still is very odd. Also there is no sign of the fog rising off the lake being anything other than quite calm winds, again unusual on the ground near tornado type activity.
I'm not being too picky, but if someone is going to say this is a funnel cloud or twister in the making, that it is that. I looked for other notices on this photo and didn't find any, but am fascinated by what comes up from time to time, so I'm hoping more information about this photo, rather than the scanty info given from the Royal Society, can lead to it's real formation.
So while I think the photo is real, it isn't a twister as of yet. I was unclear, perhaps, in whether or not the picture was real vs. was it a real twister in the Yukon, which does happen. I think the google response was for one in 2010.