John "JG" Giannandrea was hired over to Apple around 2018 to head Apple's new AI/ML division, which would include the Siri organization that predates Giannandrea's tenure at Apple. Giannandrea was previously the executive in charge of Google's Research division.
Mike Rockwell was hired into Apple from Dolby Labs around 2015 to head a group called "TDG" that would be the R&D and the product group for what we know today as Apple Vision, an AR/VR headset. The same organization had its own AI/ML applied research teams focused on computer vision problems, and had hired in folks from Microsoft's Hololens team.
From what the article describes, the Siri organization is being moved from Giannandrea's scope to sit under Rockwell, and Rockwell will be moving away from the Apple Vision organization.
Apple hired Giannandrea to build an organization like the one he led at Google, and appears to have found that that the AI/ML organization built at Apple struggled to manifest its work into successful product wins despite the massive financial investment. It's worth noting that at Google, Giannandrea was succeeded by Jeff Dean, and the organization was more recently reorged to become the "Google Deepmind" we know today also had the same struggles.