Frankly, I also didn't think that Barcelona would only get 1 point in this match because their squad is much more promising than Rayo Vallecano, and Barcelona also has a good record when facing Vallecano. But in football, surprises often occur, and that is what happened when Vallecano surprisingly managed to hold Barcelona to a draw. Barcelona's rhythm looks quite monotonous and they failed to dominate the game, and they didn't even have more shots on target than Vallecano.
This is where the unpredictability in betting lies, there are matches like Barcelona vs Rayo Vallecano, when almost no one doubted that Barcelona should win, but instead there was a draw, which spoiled the bets of many players. It is difficult to say what was the reason for this draw, Rayo defended well and were able to equalize at the end of the match, and Barcelona could not score again, this happens sometimes. I think that this is an exception to the rule, and in La Liga, few will be able to take points from Barcelona.