Hmmm. Interesting as my mum's dog (lived to be 13, never had a day's illness and died in her sleep) used to have garlic tablets - as recommended by the vet!
It's very controversial - just do an internet search and look at how many conflicting articles there are. I wouldn't panic yet as an awful lot of dogs have eaten garlic over an awful lot of years and come to no harm.
I'd be interested in seeing the research that "proves" this (though I probably wouldn't understand it!), I wonder if it's like the recent study that says anti-depressants are no better than a placebo in moderately depressed people - the one that contradicts every other piece of research going and yet got splashed across all the papers