I thought that was in The Truth of the Lie but it wasn't so I don't recall which of the umpteen things I've seen and read where it was mentioned. They were looking for DNA from Madeleine and could find none in the apartment so had to retrieve something from the McCann family home and that was her hairbrush. Diasi may well have seen this reference and recall where.
Same as you, I saw it in the copies of the PJ Files posted on the original McCann Files site before it was taken down after legal action intimidation.
Fortunately a lot of his material is on the McCann: JP Files to which you have linked & thanks for doing that as you've saved me the job of finding them.
Questions have been asked as to why Gerry McCann was dispatched to the UK to collect a sample of her DNA, in this instance hair from a brush, as there's no proof it was her hair at the time it was collected.
The DNA sample should have been collected by the UK police or, on second thoughts, by the Portuguese police.