In that same paragraph it says "remain open to the idea of re-signing next summer"Here's Amick reporting that George has made it known that he won't "close a window of opportunity" if he lands on a contender: https://www.usatoday.com/story/sports/nba/2017/06/28/paul-george-warned-indiana-pacers-trade/435476001/
That is nowhere near the ballpark of "George would be willing to sign a three year extension in Boston."
There is no realistic way for George to sign an extension with Boston if they also sign Hayward. That's before even taking into account Georges' willingness to sign an extension.