For what it's worth, I thought there was a very slight touch of the ball by their keeper. You can see a slight deviation in the direction of the ball from at least one angle. It was after Foden kicked the ball.
But it is irrelevant. Nowhere in the Laws of the Game does it say a foul cannot be committed if a player touched the ball in the same action.
A foul is committed if a player kicks an opponent in a careless or reckless manner, or using excessive force. That foul definitely met those criteria, and it was a penalty.
All this 'did he touch the ball' nonsense is just obfuscation. As is the stuff about going to ground or staying down. A foul is a foul, independent of anything else.
In fact, by trying to stay on this feet, Foden definitely did the right thing. This is because he might have scored, and we wouldn't have needed the penalty, but if he didn't, the referee could have brought play back from the advantage that didn't accrue, and award a penalty anyway. This is what should have happened, giving us in effect two bites at the cherry.