There are many surprises in football and this is one of them and it must be admitted that Rayo Vallecano is a strong team when playing at home but if we measure the strength of both teams it is clear that this is a big surprise that happened at the beginning of the La Liga season this season although we should not be too excessive because on the one hand I see Barcelona as if they were unlucky so they could not bring out their best performance so I will not also respond to Barcelona's performance because in my opinion from this one match cannot be used as a reference for anything.
I do not agree with that at all. They are not a strong team and you will see end of the season they will be much lower. The only thing is that not even the greatest team ever ends up winning all their games. Look at Bayern when they won six cups in a year, look at Barcelona when they won six cups a year. That is the most cups a team could win in a single year (English teams 7) and yet they still had losses and draws during that year.
Just because one game ended in a draw, doesn't make Barcelona bad, and doesn't make Rayo good. It was just one of those games, everyone ends up losing to everyone and it's common thing. In football ,bad teams could end up beating the good teams, it happens and it is not rare, and this was one of those weeks.