Because people understand that idea on a basic level, they sometimes make the mistake of thinking that if they were to meet a troll in real life, that person would most likely turn out to be a nice person. They're not sadists, they're just internet sadists! But what the Manitoba paper suggests is that a shy jerk who becomes unshy when they're online is probably still a jerk.
The non-academic proof for this is the story of when comedian Chris Gethard tracked down a guy who'd left a bunch of nasty comments about him online. Gethard does a video interview with the guy, Travis, and Travis turns out to have the personality you'd expect after reading the Manitoba findings.