Hensch gave the drug to a group of healthy, young men who had no musical training as children. They were asked to perform tasks online to train their ears, and at the end of a two-week period, tested on their ability to discriminate tone, to see if the training had more effect than it normally would at their age.

In other words, he gave people a pill and then taught them to have perfect pitch. The findings are significant: "It's quite remarkable since there are no known reports of adults acquiring absolute pitch," he says
So, given suitable training, peoples musical ability improves. WOW! what a breakthrough.
Apart from thet little "than it normally would at their age" I see no 'control' group for comparisons.

It doesn't sound very scientific to me.

Also it seems to be swapping the terms 'perfet pitch' & 'absolute pitch' almost at random.