My kids dad that they rarely see (his doing) has quite the dysfunctional family. His mum has never met my kids, they were in nicu in hospital and even though she was two streets away passing through down did not bother come to see them.
Anyhow their ‘grandma’ their dads mum managed to get hold of photos of the kids from my Facebook and had them printed and put them up on her wall! I only know this because she kept coming up as people you may know on fb and the pics were in the background of pictures she posted.
I have asked her for her address to send photos years ago and her reply was she doesn’t want to know anything about my putrid kids! I replied saying she has my contact details if she changes her mind. I don’t lower myself to their bs.

If you have no relationship with them, then yes it is wrong of them to claim to be your childs grandparent.

I guess genetically speaking they are still related as grandparent.