I think the performance of a team in a particular match can be used to evaluate how improved they have become and winning an important match can also serve as a Moral booster to a team and I think the performance of Barcelona in that game shows somw sign of improvement even though they have not really been so good this season but winning the game to move to the second place in the league ahead of Girona can help them to also do better wheb they face Napoli at home in the champions league.
ThIs is very true especially if in subsequent games the team has been of very bad performance and have not been able show a good performance in awhile, when next they are up with a good performance it will be measured that they are now in a better form than they were previously but then it's not all the time that this assertions could be correct because it could be the team is yet to improve but are just playing against a weak side.
There are some teams that even in their weakest form they will still be able to win some other team because such team is considered weak and doesn't have the capacity to really win the other especially teams that just git promoted from second division, they usually struggle at the earliest part of the season until they will be able to get pass that weakness and will then eventually get a new form and probably get to be better and perform well but some other literally struggle through the Season and may not get the opportunity to go far much above the relegation. The improvement seen with Barcelona to me seems like they met a weak team thst was why they were able to put up with such a performance but they may not be able to get away with such performance in the champions league.