Where and when was this certificate found? (It might be a regionally specific thing). How bad is the handwriting - the possibility of ND for "natural daughter" comes to mind.
During some time periods pressure might be put on the mother, especially if she was on parish relief, to give the name of the father. (thinking say early 1800s and earlier in England, for example). In this case the man might be listed as "charged with bastardy" (basically it was to make him pay so the parish didn't have to support his child).
There may be records relating to this surviving in local records offices.