So I had to get up and change entirely and fed a whole another 5oz bottle. When I washed the bottles in the morning it was full of powder he said yes couldn't shake it properly as was leaking
So you took over to fix a mess his incompetence had caused, instead of letting him deal with the consequences.
Him not understanding that the bottle leaking is a sign he's done something wrong means he truly doesn't know what he's doing.
I don't agree with other posters that this is strategic incompetence, I think it is actual incompetence based in inexperience (and ignorance in the reusing bottle scenario.) You can either instruct him or not, but you need to leave him to do it, and deal with the consequences of doing it wrong, so he can learn.
It may be an easy task, but it's possible for anyone to be incompetent at an easy task if it's not something they've learned how to do.