That is because you, or a previous owner, has loaded a custom boot animation into the flash memory, and Hijack knows to look for that.
Are you sure?
Check for yourself with the latest Hijack --
LittleBlueThing has contributed a
Boot Graphics selection to the Hijack menu to show the
boot animation as well as the built-in
empeg animation.
I could have sworn that Hijack includes its own non-factory boot up animation. Didn't you sort of have a "contest" at some point, and Mike Schrag's animation is the one you decided to permanently include in Hijack by default?
Ancient history, I'm afraid.
-ml