What you mean to say is that it doesn't fit your concept of a startup. There's no single definition of "startup" that's commonly accepted. In my view Facebook is at the very extreme end of the startup spectrum.
By such logic you can almost call Google a startup, or any other IT firm really. What exactly makes Facebook a startup by any definition?
When it slows down and settles into long term strategy it will cease to meet my definition. It's starting to do that now.