So hard to defineI think if children are not in school, and learning "school skills" they are homeschooling. It's hard to define school skills but they include learning letters and numbers.
A six month old can't be homeschooled but a four year old may be. If the parent wants to unschool and the child is unmotivated (perhaps due to some bad school experiences in the past) and chooses to watch music videos all day long, I don't consider that homeschooling. That is just a school drop-out.
If unschooling is done sucessfully, I consider it a method of homeschooling. If the child learns to read and write by using grocery lists and road signs, she is still learning school skills. If a child learns about the civil war by watching videos and going to a museum she is learning history. It's not as if a child must use textbooks and worksheets in order to learn. I don't know if unschoolers want to be called homeschoolers, but I consider it a type of homeschooling.