I should really add that uncertainties like this are why people should ONLY go to reputable breeders who follow health protocols. A good breeder could explain the difference between MVD and flow murmurs and talk through options regarding a puppy with a flow murmur and not leave a potential buyer feeling concerend or lied to. I don't know whether this man is a breeder or selling on a pup from elsewhere but if he isn;t affiliated to the club and doing standard testing I wouldn't take a pup from such a source anyway. Contact the breed club for references for good breeders that health-test.
Look at it this way -- the least worry you have is a puppy murmur if it is a flow murmur in a puppy bred by a good breeder following heart protocols. If you buy from a breeder who doesn't follow them, you statistically have at least a 50% chance that your new pup will have a murmur anyway in the next few years and it is more likely to be a serious murmur. Stdies show breeders who follow heart protocols and other good health breeding guidelines produce puppies that are considerably less likely to get a murmur until old age.