No don't think the vet is palming you off just that as he is young the most obvious I think would be a growth murmur. If it is still there at 12 weeks the vet will probably advise further tests just to be on the safe side.
A vet can only tell you that they can hear one but not tell you what is causing it which is why if still there at 12 weeks they will probably advise for further tests. Hope that explains it a bit better for you
