Nene's ninth-minute opener was cancelled out by a Gonzalo Higuain penalty in the first half as Napoli could only collect a point in the Serie A clash.
Benitez's men missed a chance to close in on Juventus and could enter the Christmas break 10 points behind the leaders.
The Spaniard labelled the pitch 'horrible' but said a draw was far from the worst result against the 11th-placed Cagliari.
"In all honesty, it was difficult to play and move the ball around quickly on a horrible pitch," Benitez told Sky Sport Italia.
"We created more chances than Cagliari, but it was not sufficient, as we should've scored two or three goals.
"It was a very important match for Cagliari in front of their fans. In theory a draw here is not a bad result, but it is for us because we're chasing the top of the table, even though it was very difficult here.
"The ball did not roll evenly, so we had to go for long passes and this created a gap between attack and midfield.
"Cagliari had few scoring opportunities and the defence was strong tonight. If anything, we were lacking in attack rather than defence."
Benitez insists he is unfazed by the points gap to Juventus, who host Roma on January 5 in their first games back in the league.
He said he just wanted to see continual improvement from his side as they aim to qualify for the UEFA Champions League.
"The only thing I am worried about is seeing the team continue to grow. We know there will be Juventus-Roma in January, so we must focus only on our own results," Benitez said.
"We have one more point than we did yesterday.
"We are doing better than last season even after playing the Champions League, so what more can we do? There are bound to be occasional mistakes, but this team is growing."
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