Yes indeed, Rayo Vallecano is not a completely weak team, and although Rayo Vallecano lost to Barcelona but Rayo Vallecano is also still in the top six of the La Liga standings this time. In addition, based on head to head records, the fact is that Rayo Vallecano rarely lose with a big score against Barcelona. So yes, the victory with a score of 1-0 is still a good result for Barcelona, because only with a narrow victory it is enough for Barcelona to still be able to stay at the top of the standings. I also only bet Barcelona -1.5, in fact still lost, but I still accepted the results.
I didn't bother checking the odd for the match between Barcelona and Real Vallecano as I felt it will be too small, but I'm surprised to see that Barcelona was even given up to 1.58 odd. If I had seen this odd, I would have given Barcelona a won in that match because I had the confidence that Barcelona will won the match to close in on Real Madrid. Although it was not an easy win because Real Vallecano gave them serious headache in that match unlike what was expected.
For Barcelona's winning odds themselves are very small, which can be ascertained that Barcelona will win the match, but looking odds at Barcelona -1.5 @1,58 it can be ascertained that it is too risky because Rayo is not a weak opponent and Barcelona certainly cannot score many goals in the match and it is true that Barcelona was only able to score 1 goal to get 3 full points, in a match like this I would rather bet on the total Asian under, but if the one facing is a weak club, I might dare to bet on Barcelona -1 or -1.5