I've looked at the statistics for this match & Rayo Vallecano dominated the attack. Both Barcelona & Rayo Vallecano had the same number of shot attempts, but Rayo Vallecano had the most shots on goal (6 shots on goal). I don't know why Rayo Vallecano could play so aggressively, maybe playing at home boosted the morale of the Vallecano players.
With this result, we only have 2 teams remaining in La Liga with perfect runs, they're Real Madrid & Athletic Bilbao. I hope Real Madrid maintains their consistent good results so they can secure La Liga title this season.
Rayo was truly able to match Barcelona's game plan in that match. In fact, Rayo played more effectively in that match. Because although Barcelona had more possession in that match, Barcelona actually struggled to build attacks into Rayo's defense. However, Rayo, despite losing possession, generated as many attacks as Barcelona. Furthermore, Rayo also managed to register more shots on target. So, it seems that being the host team did boost the players' confidence in that match and allowed Rayo to play better than usual. Meanwhile, Barcelona seemed to struggle to develop their own game plan.