Around here, that last is far from true. Here, most RPG tournament events are about the same sort of games you'd expect to play in non-tournament environments. You're expected to read the character sheet and play the character as indicated. If you're character sheet doesn't indicate that you knew the other characters well at the start of play, you wouldn't be telling the other players everything about your character at the start of play. (Besides, if they were supposed to know something, they'd have it on their character sheets.) Sometimes you might get a further warning from the GM, but that's when the secrecy is particularly important, even above the norm.Some tourneys are character interaction focused where you have secrets that must be maintained for some or all of the event. Sometimes characters are given secret motivations or hidden goals. These will be listed on the character sheet and usually the secretive nature of the tourney will be explained first by the DM.
We do have RPGA events here, and those are a different kettle of fish - so much so that many players avoid RPGA events, or avoid non-RPGA events.