I think it's invasive enough that they expose your usage of muse to your instagram mutuals without consent. Parts of my circle are very anti-AI and I would not want them to see me mentioned in a 'x, x and x are already on muse' ad on instagram. This example of yours is mind-boggling in an entirely different way
I imagine meta wants to make it easy to connect to "your" account in the same house if you have multiple devices.
Don’t know how it would cause Meta’s auth to show me other peoples accounts. I looked up some of the people and they seem to be other devs. It obfuscates email addresses but most are in a format that’s not hard to figure out [name] @ [name domain.com]
Just more Meta sloppiness from what I can tell.