Does this man’s paradoxical thought lead him to believe that all roadways are simultaneously both black and white, and therefore step off the sidewalk any old where and get run over? Surely not, since the zebra crossing is definitively stated as the location of the man’s demise.
What I’m trying to say here is that the joke doesn’t quite work.
i think it is more that he actually proved black was white (just as he proved God didn’t exist, and therefore God did not exist), his ‘proof’ actually made it so. this is a paradox, and when he encountered this paradox (at a zebra crossing), the paradox destroyed him.