I am extremely upset by the hostile undertone of that reply.
Seriously though, it was not my intent to offend you in any way, so I'm sorry.
The question didn't strike me as rude or sarcastic, but then I'm not a native speaker, so some subleties of English might escape my grasp.
And uh, no, I'm not ungrateful or anything. How could I be for something I'm getting for free?