I was thinking about it. The only place where the app was still installed was an Android tablet but no one has opened the app for many months (only me and my partner has access to the tablet and none of us opened the app). It could theoretically connect from the background by itself (I think android makes it possible for apps to run in the background) but when I tried to open the app the day after I got that email, it just displayed Update required screen (we don't auto-uldate apps on that tablet). And the suspicious login mentioned in the email was not recorded in the Recent Activity in the profile. Unfortunately I don't record all network activity on home network so can't 100% rule out this possibility but it seems unlikely to me that the app would try to connect from the background after couple of months by itself.
The email I received was "We’ve detected a suspicious sign-in to your Netflix account. Just to be safe we've reset your password and you’ll need to set a new one." with a button to "Set a new password".
It didn't mention any IP or geolocation as many other services say in such cases.