en.wikipedia.org/wiki/Quintillus

A source on Quintillus' own titulature directly contradicts this claim. The De Imperatoribus Romanis entry notes that a military milestone from Quintillus' reign (ILS 573) gives his official titles as: "Imperator Caesar Marcus Aurelius Claudius Quintilus ... Pontifex Maximus ..." If Quintillus was officially styled Pontifex Maximus, then the imperial identification with that office had not been abandoned during his reign.

A broader scholarly source also places the abandonment of the title much later. Alan Cameron's article in The Journal of Roman Studies says that the title pontifex maximus was "held by every Emperor from Augustus down to Gratian's own father, Valentinian," and discusses Gratian's later repudiation of it in the late 4th century. That chronology is incompatible with a claim that it was abandoned under Quintillus in 270.

So the statement is wrong on the historical timeline: far from being abandoned under Quintillus, the title is attested for Quintillus himself and continued in imperial use for more than a century afterward.