I don't know what kind of proof you want, but I just looked at my phone settings after reading your comment. The exposure notification option is there and it's off. The region selection is grayed out because of it. Yet I got the app (uninstalled it after I saw this on hacker news).
I did get a notification when it got installed but I thought it was just a push similar to amber alerts. I didn't realize it installed something at the time.
I'm in Boston and it wasn't installed on my phone (exposure notifications have always been off AFAIK). I'm on old iphone 5s, not sure if that makes a difference or maybe just specific areas? According to this, https://thesomervillenewsweekly.blog/2021/04/05/massnotify-a..., different cities were piloting at different times, although it all seems opt in.
Same here. Never opted in, just checked and that hasn't changed. I hadn't even selected a region, so it shouldn't even know which invasive app to install, but I still got it.
I did get a notification when it got installed but I thought it was just a push similar to amber alerts. I didn't realize it installed something at the time.
Still, exposure notification was never turned on.