@shiirosagi
no no, check the previous chapters, there are 2 hints to which you need to pay attention. Blue colour which means that owner of blood is Calisto. And some additional sparkling effect that comes when father used his blood. I don't get the exact thing about how it's different, but that due to that sparkling priest was 100% sure that she is HIS daughter. Aka exactly HIS, not father's, not some uncle's, but his.
If not for that, he wouldn't tear his hair out about "how he could conceive a daughter without even any memory of being with a woman". Otherwise, he would just leave the situation as a "secret child of my late father", and wouldn't think about it any further. But test, apparently, give more information than just "owner is Calisto" kind of thing.