The check mark is believed to have been created during the Roman Empire. “V” was used to shorten the word “veritas”, meaning ‘truth’. This was used to indicate yes, true, or confirmed on items in a list.

The simplest means of indicating verification or correctness is a single stroke, hence a tick or check mark. Striking through is a simple pictoral means of negation such as the struck through cigarette in a No Smoking sign. So X is basically a struck through check mark or tick indicating incorrectness.