Perhaps his milk consumption has gone down since he's being weaned and he's not getting all the calories he needs from milk during the day?
DD2 only slept through (at 25 weeks) after giving her bottles of milk at night so I could see how much she was drinking. It was only an ounce or two at most at each waking so I stopped going in and she stopped waking after a couple of nights.
Waking habit rather than waking for food. She actually only mooched around on each waking and then went back off to sleep after about 5 minutes. I didn't have to let her "cry it out" or anything. I just needed to leave her alone to go back to sleep. I stopped using the baby monitor so I didn't wake at every sound after that.
She still wakes in the night - she's 11 months now. Usually around 1 and 4 and she'll cry out sometimes. I just have a listen to make sure she settles again.
I'm not saying that's definitely going to work for you - just be aware that babies wake frequently in the night and it's not always because they're hungry. They do it anyway. When we're breastfeeding, I think it's instinct to jump up and feed them, partly because you can't really be sure how much food they're taking on.
I think the imagined correlation between formula feeding and night sleeping is probably more to do with parents of bottle fed babies being able to realise that their babies aren't actually hungry.
If you go to them when they don't actually need attention (ie, dirty nappy or hungry) then you actually reinforce the waking habit.