Recent research sets the LD50 (lethal dose at which 50% of subjects die) of garlic in dogs at approximately 5 grams per Kg.
So the dog who got sick from eating a whole bulb of garlic may have gotten a dangerous amount if the bulb was 50 grams like the ones I buy and the dog was 10 kg or so (22 lbs). Smart per owners will keep all medicines, natural or not, in a safe storage.
That being said, much valid research seems to indicate nothing but good effects from a clove of garlic a day for dogs (use Google Scholar to search for and see all the papers on the web). For tiny dogs a tiny piece is likely all that is needed.
My Thai Dog puppy loves garlic, but as he only weighs 12 Kg at 5 months old, one clove a day is all he gets. The vet says he looks great and tests show no intestinal worms.