You're right, that is a no-no of the 1st order. I don't recall watching that game, I was in HS, but I was indeed a die hard Mets fan. Everyone loved Bunning that day!
It was great to see the Mets fans happy to see the great performance of a Phillies pitcher.
I remember hearing once, former Yankee Elston Howard, said the only time he was booed in Yankees Stadium, was when he got a base hit to break up a no hit bid by a Red Sox pitcher. He got that hit with two out in the last of the ninth. With the Red Sox ahead 6-0, there was no way the Yanks could pull it out. But those Yankees fans were rooting for Bill Rohr to close out the no-hitter.