Drew has posted a response in defense of these allegations.

Having read it as well the "report" on him you linked, I personally find the report lacks credibility. I take much more stock in Drew's accounting of things, including his mature ownership of the bad decisions he's made in the past.

As for the Stallman Report: it's not a smear piece in my view. It's a whistleblow that outlines an argument why RMS is unfit to lead the FSF with accompanying evidence. You may disagree with some of it, but it's hardly malicious; I can sympathize with anyone who wishes to see better from the leaders of the major social movements of our day.

And as for why Drew initially denied his involvement, I found his response reasonable:

Myself and the other authors asserted our moral rights to publish anonymously, motivated by our wish to reduce our exposure to the exact sort of harassment I’ve been subjected to over the years.