This is VILE.
Breastfeeding is about nourishment.
Not validation of the person feeding the child.
That baby had adequate nourishment from its own mother, via breast or bottle.
When have you ever heard of a Grandmother breastfeeding her grandchild?? In modern times, never, because women do not feel the need to do this!!
Especially when there's absolutely no reason to.
This is selfish and perverted.
Did the mother know?? This is child abuse pure and simple.
If anyone walked in on a 50yo man putting his nipple in a baby's mouth the police would be called.
This CANNOT BE JUSTIFIED IN ANY WAY.