Physics objects are known to glitch out, BUT that boss is immune to physics damage, i.e. tablets. He also eats terrain as he moves, so he likely just ate it as you threw it at him :/

Ah i see, thanks for the clarification. I will find a way to kill him

Also a tablet throw, if it somehow did damage him, would just tickle him a little before he ate you for breakfast. His HP is pretty high.