I believe whoever first brought up Ronaldo returning to Man United here, he must have made it up. I didn't even find which media spread the rumor about Man United and Ronaldo. Logically I agree with you because it is very unlikely that Man United can give a bigger salary to a player who is already old even though he is a star player, but surely Man United management will consider not bringing the player back to the team.
This too have been a point of concern to me honestly, I have looked around to see which media peddled the return of Ronaldo but I am yet to see any, and no verified media has ever mentioned anything that suggested such, so I agree it's obviously this persons taught and maybe the person wished such happen and taught to bring it up for discussion. Manchester United may still like him but will not want to bring him back and not even with the high pay, they will rather skip such deal.