A reporter from The Guardian at the game noticed the doves crash land into the stands.
It might be a bad sign if soccer fans in Brazil were superstitious (they are). Also it would've been another bad sign if Brazil opened the tournament with its first own goal in the history of the World Cup (they did).
Another thing that is not a bad sign is that Brazil did the exact same thing the last time it hosted the World Cup, in 1950. Hundreds of pigeons were released right before the opening kickoff against Mexico. Brazil didn’t win that tournament and it was a bit of a national tragedy.
At least the third dove is ok.