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So my question is, what happens when you throw a Boulder Bullet at a target?

A boulder bullet appears to be a magical sling bullet when held, but it is actually a shrunken piece of catapult ammunition.

A boulder bullet expands rapidly when launched from a sling or sling staff, increasing in size and dealing greater base damage depending on the version used. This doesn’t affect the bullet’s range or any of the normal mechanics for using a sling bullet, though the boulder bullet is treated as siege weapon ammunition for the purposes of wind effects and similar penalties. Similarly, if a boulder bullet is launched and misses its target, roll 1d8 to determine the adjacent square in which it lands. Once it has been thrown and has expanded, a boulder bullet loses its magic and remains boulder-sized thereafter.

It says that it expands after being thrown too, despite it referencing a sling or sling staff in the beginning. Did they just put the referencing to the two ranged weapons since it's originally a sling ammunition, or would it actually work when thrown as an improvised ranged weapon too?

So, this got me really confused, and would love some clarification.
Ghost syrup makes you Incorporeal (Ex), which says in the first line:

"An incorporeal creature has no physical body."

Do you become an undead or a humanoid incorporeal? Like what even are you technically when you are incorporeal, do you become like non-native outsiders whos souls are their bodies?

Secondly, since being incorporeal, you have no physical body, does the ruling of Incorporeal Possession count for leaving no body behind during possession?

"Ghosts, shadow demons, and similar creatures do not possess physical bodies. They are simply disembodied souls. They use the rules below to govern the interaction between their mental characteristics and their hosts’ physical forms. Such a creature merges with the host’s body and is unharmed when ejected. Creatures that use magic jar can often use the new possession spell instead."