I would try to encourage him to eat if you can, even if it's higher carb food. I think moderate ketones is significant that you should do what you can to get them down. The strips are accurate in that they will tell you if ketones are present, they are inaccurate in that it is telling you after the fact as that urine ketones could be from an hour or more ago and thus the ketone measurement is not reflective of what is happening
right now. A blood ketone meter would be real time, obviously.
By all means, give fluids as directed, I'm just sharing my experience with you, Asia was on fluids.
Ketones and DKA can happen fast. They can seem fine one minute and some hours later be in trouble.
You do not want to skip insulin if you can at all help it. The recipe for DKA is not enough insulin, infection and not eating. Get food in to him any way you can so you can give him insulin.
There lots of people with DKA and ketone experience on this board, they can help.