Let me answer some questions based on my experience with the snap store.
The metrics are based on how many devices check for updates to the snap. The region information is an approximation based on the timezone of the device. Afaik, IP addresses are not recorded.
The publisher can choose to turn off the public display of the metrics in the listing page, though the publisher will always be able to see the metrics themselves.
At the moment, there does not seem to be a way to opt out of the metrics, but I haven’t seen many people ask for it, so it might just be due to a lack of request for it. The snapcraft devs are very responsive on https://forum.snapcraft.io, so if you care about opting out, it might be useful to respectfully engage with them there.
Though it’s important to keep in mind that this kind of data is collected by most package repositories. The snap store is one of the few that actually shows these metrics publicly.