I mean, sure, we don't know 100%, but at present the only narrative link that they have confirmed is that BG1/2 happened 100 years ago and people remember as history to varying levels of accuracy. We know that the Dead Three are involved.
But, that just confirms that BG1/2 are cannon. So is the Underdark and Menzoberannzen. The existence of Forgotten Realms deities doesn't necessarily make it Baldur's Gate.
We know 100% certainly that the Gorion/Jon Irenecus story is FINISHED, completed, and done. Adam Smith goes to great lengths to point out that this is a rare thing when making a sequel, which has freed them up to make new stories and characters.
Imagine if Disney had called Mandalorian "Star Wars 10" just because it features the empire and a throwback to Yoda, and it takes place 50 years later.
It doesn't really matter who made the decision to call it BG3 .. it was a marketing decision, not an artistic one. That's why I call it a low blow.
