Hi...no, I would not be concerned...unless you are buying your puppy with breeding rights and intending to breed...then you might want to find out if this was a one time thing or if there is a problem with the mother.
But sometimes nature causes some strange things and I have heard of single births quite often.
As far as having a C section, there could be many reasons for that as well...the pup could have been sideways in the tube and not able to get out...so, I wouldn't be too concerned for the health of the puppy, unless there is something about the situation that I don't know about...