Oh balderdash! Who says that male arousal following the scent of testosterone is not, itself, a learned response? In other words, if you have engaged in homosexual behavior, i.e., initially abused as a child by a male adult, and then later acted out that behavior, then perhaps you have "trained" your brain to respond in a certain manner that is different than the norm. That is, who is to say that ones brain response came before the learned behavior?
Notice that Witelson is NOT one of the researchers. This was a person hand-picked by the journalist to interpret the findings in the way the journalist wanted it to be interpreted. The researchers DO NOT claim that homosexuality has a biological cause. This is a biased article, putting words in the mouth of the researchers. Notice they don't quote the actual researchers until far later in the article, and when the researcher seems to imply homosexuality has a biological basis, he is paraphrased and not quoted.