The law has always ( at least in my lifetime) been that you are offside only if your own player was the last one to play the ball. It was however clarified more recently that an opposition player had to deliberately play the ball, rather than a situation where he has no control of it.
For example, let's imagine Rodri was in an offside position, the Villa keeper has the ball and throws it to Mings. Mings isn't looking however, it hits the back of his head and rebounds to Rodri, who is then judged to be offside as Mings is judged not to have played the ball deliberately.
If Mings is under pressure from a player who's onside, tries to head it back but heads it to Rodri, that's not offside. If Rodri challenges Mings for the ball before or as Mings plays it, he's offside.