Apologies for the poor quality, this is the only footage I could find off a quick search.
So - yeah, could have headed back to Ederson. But he is quite central and Bailey's on Ruben's heels so that option isn't risk free - too strong a header and he's making Ederson save him from an own goal, too weak a header and Bailey charges it down and has a one on one with the keeper in the box (note Ruben is facing away, so would see the ball after Bailey, in which time he could be passed without the opportunity to beat him to the ball).
Can't head it to Ruben or Cancelo for the same reason - Bailey's well positioned to intercept, and Watkins to pick up any second ball if they miscontrol. Walker's behind him and being closed down by Coutinho so that's a no-go too.
So the pass to Rodri - central, but pushing out a good distance away from goal - isn't actually a huge error, I don't think. It should be a safe pass.
Rodri's poor control, and decision to blindly pass back to his left into Villa traffic, instead of turning right and passing either to Cancelo or the midfielder behind him, is probably more of an error than Stones's header.
All in all I think Villa worked the goal well and it's harsh to blame it on Stones when his options were limited, Rodri subsequently lost the ball, and Cancelo probably should have closed Bailey down quicker.