Is it permissible to swear that what a person recites without tajwid is not the Qur’an?

It is not permissible to swear that what is being recited is not the Quran, unless the لحن (melodic error/deviation in recitation) in it significantly alters the meaning and does not conform to any of the متواترة (transmitted through an uninterrupted chain of narrators) recitations. In this case, whoever swears such an oath would be truthful in their oath.