I don't know whether this is the clincher, but I think it is.
It shows Mings about to play the ball with his left foot, AFTER he has chested the ball down.
Rodri can be clearly seen to now be onside - check out the position of the Villa number 2 (and Rodri has not yet touched the ball).
View attachment 114894
So: prior to any contact Rodri made with the ball, he had got himself back into an onside position. That is clear from the above. He had not obstructed or prevented Mings from getting to the ball - that is 100% true. Mings had already got to the ball and chested it down without any interference from any Man City player.
Onside. Perfectly legit goal, and what a cracker it was!
I think some people on here are getting confused with the scenario of 'Player A' playing the ball forward, and 'Player B' of the same team being in an offside postion at the moment 'Player A' plays the ball forward, but by the time 'Player B' touches it he is ostensibly 'onside'. No, at the point of the ball last being played, 'Player B' is offside. Last night, at the time the ball was last played, Rodri was onside, as evidenced by my earlier screencap, and the above.