It's allowed to be highly coincidental, because it's only these ones that end up as UFO photos, which is a very small number.Man in a boat is possible I suppose, but the comparison above doesn't look much like a plane. It seems highly coincidental that the photo was snapped at an exact moment where a fisherman was posed such that he and his boat looked indistinguishable from a plane.
Is the dress blue or black? Seems highly coincidental that someone would take a photo under just the right conditions so that people would be totally divided about what colour it was. But that's why that particular photo got such attention.
You're highly unlikely to win the lottery, but it's highly likely that someone will win.