Sounds like some sort of secondary fermentation started up. What was the sg when you bottled it and what type of yeast?
You say is was completely dry so if the sg was close to terminal, then you might have stirred up just enough action by the yeast when you racked to get some carbonation, probably not enough to make much pressure. How sure are you that it was dry?
You can always keep testing them every few days and if the pressure starts getting high, refrigerate or pasteurize them. probably wouldnt hurt to put them in a cool place