Well, that Google Play acc is connected to another HM account, which is why I got this notice. I use the same Google Play account on other instances and on my phone. The only time it doesn't appear is on the device with the modded app and where the HM acc linked to this Google Play acc.
The vanilla port will always autolink to your Google Play acc. But, not that it matters if you're using the modded app. I'm just sharing since I use vanilla on emulator and the app always tried to connect with my Google Play (and then failed)
No. Because it's another google play acc, so this notice won't show up. But if you have a vanilla version on another device or instances on emulator (with another google play account), the app will autolink to your google play the instant you open the game.