Ok..I will amend a couple things from the previous post.
They might not know the definition of the word fantasy through no fault of their own. Good news. That is in the dictionary and can be provided.
They, somehow, might not know that D&D is a fantasy roleplaying game. I think that's already pretty clear from everything down from the cover of the book through to the end of the introduction. Nothing more should need to be established there other than that players should look at the stuff.
If, after receiving the definition for the word fantasy and the knowledge that D&D is a fantasy RPG, they insist upon using real world expectations to guide what "should" be possible in the game mechanics..
..then that is acting in defiance to what the genre and the game says about themselves.
Edit: if I go to the pool and someone hands me a pool toy, it's my fault if I insist they spray it with a hose before I can use it in the pool (or else it wouldn't be wet)