That's actually an unprovable statement which has gained popularity party because of the fallacious premise that women don't like about rape and partly because there is no reliable record of false rape accusations in sexual assault/rape statistics outside of those that allegations that are disproven once an arrest is made and the case goes to the prosecutor's office for consideration. Even then the FBI has deternimed roughly 8% of all rape/sexual assault allegations are proven to be unfounded, and while that number is small it is roughly 4 times the number of any other indexed crime that the FBI tracks. Also, when one considers that the 8% number does not inlcude those allegations where an investigation took place and the police determined there was no rape or those cases where the prosecuting attorney refused to prosecute based upon the evidence in the case and/or the claimant's allegations, then determining the actual percentage of false rape claims is difficult if not impossible. Studies done have variable #'s, anything from less than 1% of rape claims being false to almost 90% being false (which is surely impossible), however the most reasonable estimates I've seen indicate between 25% and 45% of rape claims are in fact falsely made.

Given the number of stories of false rape allegations that have broken in the news within the last year I am more and more inclined to accept the premise that men are falsely accused of rape much more often than the FBI's 8% number would indicate and in this case OP seems to have evidence/knowledge that confirms that his brother was falsely accused.

That said, get a good lawyer, one who handles sexual assault cases as a specialty would be your best bet, a woman lawyer who handles that type of case is even better. Good Luck, OP, you're brother's gonna need it.