Card differentiates between "science fiction" and "fantasy" as follows -

If the story is set in a universe that follows the same rules as ours, it is science fiction.

If the story is set in a universe that doesn't follow the same rules as ours, it is fantasy.

In other words, if the people in the story use "metal and plastic" as Card puts it (i.e., science and technology) then it is science fiction.  For example, they might travel in aircraft or space ships.  But if they do the same thing using magic or the supernatural, then it is fantasy.  For instance, they might travel on a flying carpet.