That's a pretty good theory and sounds reasonable too.Everything in this post is my own speculation. I have no VMware inside information!
I assume that VMware could not achieve a late summer delivery for whatever they have planned for VMware Fusion 9. Lacking anything to announce that could line up against Parallels 12, VMware chose to take the next point release with whatever bug fixes that their developers have managed to close, ran a round of regression testing against macOS Sierra (host and guest) and Windows 10 Anniversary (guest), called it "Version 8.5" and declared victory.
I wonder when the real VMware Fusion version 9 will be released?