From the New York Times piece:
The panel's report veers from other factual records on several points, Mr. Hammerman said this was important proof that the police had not fed a story to the defendants, and that Mr. Wise was speaking from firsthand knowledge. ''We didn't know until now that one of the defendants mentioned a Walkman in a pouch,'' Mr. Hammerman said." In fact, prosecutors have long said that the victim was not wearing a pouch, belt or the kind of Walkman that would be carried at the waist. The victim had been wearing a radio headset that slipped over the head and did not attach to anything else, according to a court filing by the district attorney.
It's not nearly so clear cut that the Armstrong report is in the wrong here.
Reyes admitted to taking the jogger's Sony AM/FM headset Walkman (though not a cassette walkman that usually attaches at the waist). The jogger confirms that she is missing her Walkman. This is all in the Ryan report that vacated the prosecution, not the Armstrong report.
In the motion to vacate, the assistant district attorney Ryan specifically cites as reasoning that Reyes knew about the missing Walkman but that "None of the defendants mentioned the jogger's Walkman."
Reyes also says the jogger had a "fanny pack." The jogger says she had a key case attached to her shoe laces of brown Velcro. (This is in another part of the Armstrong report.)
The Armstrong report then says about the Wise interview notes:
Kharey Wise was questioned at 4:50 AM on April 21, 1989 by Detective Jonza, whose notes list what Wise told him regarding “persons present when girl raped.” (Exhibit E.) Included on the list is the reference “Rudy – played with tits/took walkman.” At the bottom of the page, it is noted, “female had pouch for Walkman on her belt.” Wise’s description of the walkman “pouch” is, therefore, similar to Reyes’s description of a “fanny pack.” At the time of this interview, neither Detective Jonza, nor anyone else investigating the events of the evening, had any way of knowing that the jogger had a Walkman, or a pouch.
So the interview notes show that Kharey Wise had accurate knowledge of the event insofar that she had a walkman, a guy took the walkman, and that she had a pouch. On the other hand Kharey Wise had inaccurate knowledge in that the guy was not named Rudy, and the pouch was a fanny pack, not a holder for a walkman.
The Armstrong report itself does not appear to be factually wrong in this case. You could accuse the Armstrong of emphasizing the parts of the police notes that match (the taking of the Walkman and the existence of the pouch) and overly discounting the parts of the note that don't match (the name of the guy and the nature of the pouch).