I wasn't there and even if I had been there, I wouldn't know. Depending on the dog, I might be able to make an educated guess but only the handler knows.
According to the reports I read, though, the dogs didn't stop at the bikes. They kept on going. What that means, only the handler knows for sure. As I recall, Aunt TB said the dogs went into the woods; Sandy Breault of the FBI said the dogs went towards the water.
Neither account suggests to me that the dogs stopped dead. I would be really, really surprised if the dogs did stop dead, without doing any casting around at all for more scent.