He never call Win32 an "open standard." He calls it an open platform, or open experience, which he means anyone can build win32 games and distribute them on their own.
Using the word "standard", which he never does in that article, is quite misleading.
His statement is definitively true on the software distribution side. Google wants every App installed via play store and now even Microsoft Office is only available there. Classical Windows on the other hand allows Chrome to be installed without MS acting as gatekeeper.
Yes, it's not totally black and white. Android does kinda allow side-loading with shitty usability. MS did start its own store and lets not get into telemetry. Classical windows still gives the user a lot of control, though.
They may be alternative implementations, but they're still no good in this case. See elsewhere in the thread where it's pointed out that Epic's anti-cheat software intentionally fails to run the game if it's running on Wine.
I think he's operating with a different understanding of the word "open" than the rest of us.