No, it doesn't sound fishy to me. The dog is at that age where these things are more common. I doubt the vet lied about the presence of crystals. If left untreated crystals can form into stones and this can result in a life threatening condition. Is the dog going out often enough to potty? Less frequent trips outside can help encourage crystal formation. Is the dog drinking enough? Has there been a diet change? More plant based foods cause alkalinity, meat based foods help with acidity. Too many fruit and veggie treats can throw the balance off, better to add a little canned food instead. A food change might help especially if the owner is adding stuff to make the dog food work.