Garlic fed directly in large raw quantities can cause tummy upset, but in all my findings it is not toxic unless the dog eats an entire bulb everyday for awhile. Garlic and onions are related but the element in onions that is toxic is so little in garlic that it won't affect the dog. Garlic fed to a dog can help with fleas and worms and helps support their immune system. It was not the one clove of garlic not fed directly to the dog that hurt your pup.
I do worry about Nutro Max food though. I was feeding my boys that for about a year before I found out how terrible it is for them. I have them on Taste of the Wild dog food now and its much healthier for them. My fletcher was sooo skinny on Nutromax, but he has filled out on Taste of the Wild. They seem healthier, more active and have gone from completely not potty trained to well behaved little boys. I'd get your other baby off NutroMax and feed him something better for him. I recommend Taste of the Wild, but alot of others here can give you some other really good foods also.
I am soooo glad to hear that your baby is doing better and came home. I hope and pray that his tests all come back normal with his next visit. Keep us posted.