Pirelli chief Isola told the Italian publication F1Sport: "On the 'Italian mystery', I have spoken with Wolff several times.
"He just said that Ferrari has learned to use the tyres better than Mercedes is able to do so at the moment.
"Ferrari has developed a very balanced car, in a year where the secret is to be able to have both the front and the rear tyres in the working window."
Isola said that Pirelli worked hard to develop tyres that are 'easy' for all the teams to use, but he also admitted: "It is not easy, but Formula 1 is not easy.
"It is a sport with the highest technology, and this year every hundredth of a second counts when two teams are so close."
Ferrari lead Mercedes by 17 points in the constructor standings ahead of the weekend's Canadian Grand Prix.