The recipient seems to have also done the rather over-kind thing of reccing the bizarre gift-fic. I feel really bad for them - it's not like you can anticipate your writer wants to write EATING OF RAW ORGANS into their fic, so you're pretty unlikely to include that in your list of squicks.

They should absolutely complain.

Back when I did Yuletide, I'd always include something like "just go for it, writing something you get inspired to write, without worrying about the particulars" but this kind of stuff makes me think that's pretty inadvisable..