I'm not suggesting they've deployed Stadia servers at 7,500 edge nodes or data centers. Clearly Stadia is not deployed at that scale and it is not launched worldwide.
However, it is a direct quote from Majd Bakar, Google's VP of Engineering for Stadia, that they have Stadia servers deployed at Edge locations:
“Stadia servers are deployed on Google’s Edge locations that are closest to partnered [Internet service providers]"
You're probably right that this means "Edge POPs" rather than "Edge nodes", but you are wrong to claim/assume that Stadia servers are only present at Google's main data centers.