I don't see how that would prove anything. It's not a huge leap from his previous statements to say the long-form is fake.
It becomes a huge leap if its true as a liberal plant would set Obama up to “answer” the charges of the birthers.(which is how things appear)
If Trump is saying the new BC which is the “answer” is a fake its a whole new ballgame
FWIW I think Trump is a disaster as a candidate and is not a Republican, a conservative or anything but a shyster but if he wants to and can do damage to Obama ....I wish him well