So... I don't even need to get into the merits about if this actually happening, right?
With so many cases already documented at various leagues around the world, with several players and even soccer referees punished for this, there aren't denying that there is indeed an underground market for irregular betting.

But... I am also sure there are many rumors and hearsay just to move money... coincidences or even misinterpretations by some bettors about a game that was simply "poorly played"

I've heard several stories like the one you told.... many people claim to know the result from "a friend of another friend". I just ignore them most of the time because I prefer to stick to my strategy and assume that these frauds are isolated cases these days.