He played a grand total of 6 games for Barcelona. He ripped it up for Palmeiras and again in the WC. He was not fluky.
Goals apart, he did not really stand out at the WC either. Played fine, but did not stand out as something out of the ordinary. Playing well in Brazil does not really say much either, Gabilol stands as a prime example. He has incredible physicality, i am not ruling out he could become a very good defender, but there is a significant amount of risk. Him playing so little at Barca says a lot to be honest. But it is seen before, that a player who initially struggles will still be decent, Caceres is an example of a player who were very promising but did not cut it at Barca. Anyway, i believe you are letting your home bias fuel the hype here, no certanties of him becoming world class.