There are a few things to consider, given the limited information in your post:
Are his eyes constantly watery, or was this the only time it's been noticed?
Are the other puppies eyes also watery?
If the runny eyes are constant, are they accompanied by other issues, like a runny nose or coughing?
Do other pups in the litter have runny noses or coughing?
What breed (or mix) is he? Some breeds are prone to eye problems like entropion.
If the watery eyes are constant and/or accompanied by other problems, then yes, it is cause for concern, and the breeder should have the puppy seen by a vet.