We don't need Myth Busters. I can personally confirm that vapor can set off a smoke detector... it just happened to me.
I travel a LOT (about 100 nights a year), and vape in hotel rooms as a matter of course. I've never had an issue.
But today, I was having a vape, and set off the smoke detector. I know I did because the hotel staff called my room asking if I had a fire in my room... these are all linked to a common fire panel, so they know which room's detector is going off.
I've vaped in this specific hotel room all week thus far with no issue. However, a few minutes prior, I had turned off the AC/fan unit, which I never do -- I always leave the fan portion running all the time. I suspect the lack of air movement, combined with the fact that I was vaping too close to the actual detector, was the root cause.
I'll still vape in my room (in fact, I'm doing it now), but I'll be much more conscious of making sure my clouds don't get too close to that detector.
Also, to those of you who say that "vape isn't smoke", photoelectric detectors use LIGHT to detect smoke.... vapor can and will set them off if it's thick enough to block light.