Lightning McQueen had won seven Piston Cup championships when Pixar's Cars 3 began.
Cars 3 opens with McQueen established as a veteran champion whose career is threatened by the arrival of faster next-generation racers, especially Jackson Storm. The film describes him as a seven-time Piston Cup champion before his serious crash during a race against the new generation.
That total marks a major change from the original Cars, where McQueen is still pursuing his first championship and learns that winning is not the only measure of success. Cars 3 therefore presents him as an experienced champion rather than an ambitious newcomer.
The number seven refers to championships already won before the main events of Cars 3. It should not be confused with the race results shown later in the film, including the Florida 500 and the final outcome involving Cruz Ramirez.