It always happens like that in the comics; writers present audiences with a possible origin, but they also leave lingering doubts.
It could be his true origin story, but it could just as easily be a demented story concocted by a deranged lunatic.
By doing this, director Todd Phillips will present audiences with his own version of the story (whether it’s the Ace Chemicals version or something else entirely) while also leaving invaluable room for audience interpretation.