Step parent referring to your biological child as “theirs”?

Saw a discussion on twitter between 2 women who I went to college with.

The step mom posted something on twitter saying “my child is so funny, he put stickers all over the fridge” and it was a pic of him.

And the bio mom basically shut it down saying he’s not “her” child, etc etc

My question to CC is, how would you feel with someone referring to your child as theirs?

Would you be angry, and feel like something is being taken away from you?

Would you feel glad, knowing that’s one more person caring for your child?

Would you be indifferent?