Not a big deal, but might be confusing some newcomers to inheritance when thinking about which direction (up or down) the inheritance tree one is going.
The slide says:
If the method was declared virtual, it can be overridden by any ancestor in the future.
It should instead say:
If the method was declared virtual, it can be overridden by any descendant in the future.
The ancestors are up in the inheritance tree and define the base functionality that the children further down the tree (descendants) can adjust.