Maybe that duke manipulated the results or something? Like swapping the blood of the son of rashta with her daughter's? But wow if he did that he has some serious dedication.
I can understand that but didn't they prick the children's fingers at the site of testing to make sure I think he really put that in just to torment the man cause no way glorym is his daughter remeber his infertile (which can also be retracketed by saying he wasn't infertile but has low sperm count in accounts to him and Navi eating the cookies and Navi is infertile until she goes to her new man who heals her with the bed) but anyways yeah
both children look identical, he could've swapped the children maybe? or the water could've been tampered with beforehand.
If I remember right the blood from the daughter was taken with a syringe and rashta was really sure it was his (despite her out of control delusions, self victimisation and questionable reasonings and believing always beigh right and innocent) but it may be as you said too. Just to torment him till his end. But I pity the children they are innocent.
I guess we will never know the answer to this question yet again there are many possibilities to this question as well
Didn’t they do a test to see if glorym was his kid or not? And now he gets a letter saying that she is his child wtf is going on!?