Referee Massimiliano Irrati only decided to continue the game after consulting with coaches and officials and Napoli secured a 2-0 win with goals from Gonzalo Higuain and Jose Callejon to stay top of the standings.
"I would not have stopped the match," Lazio manager Stefano Pioli told Premium Sport. "It was chanting from the minority, but I don't think they were racist.
"We also have players of colour and they are treated well."
Koulibaly, however, described the chanting as "ugly" and praised the referee in a post on his Instagram account.
"I want to thank the Lazio players, but especially the
referee Irrati for his courage," he wrote.
"I thank my team mates, the public and our fans, who have been a great support against these ugly chants.
"I want to thank everyone for the messages of solidarity
which I have received."
Napoli coach Maurizio Sarri said he was sorry about the chanting.
"Bravo to Irrati for stopping the match," he said on Twitter.
Italian football has been plagued by racist incidents in recent years, notably in 2013 when AC Milan players Kevin-Prince Boateng and Mario Balotelli were the victims of offensive chanting in two separate matches.
(Reporting by Ed Dove, editing by Ed Osmond/Ian Ransom)
