I believe this is general Throw effect ...
And i believe it has ben created to simulate momentum of and object, that has ben throwed ... no matter what kind of item it is (i believe the same is happening when you throw a potion)
I suspect it's actually simpler than that. The logic of Throw knows that both throwable and target should receive damage. However, weapons in BG3 cannot be damaged (not this way, at least). So the game applies the damage to the target, tries to apply it to the throwable, sees it can't be done and instead of stopping at this point it redirects this damage to the only object in the interaction that can receive it.
Hang on, I actually tested it. When I threw a corpse, the corpse received damage, but there was
no second entry for the target!
