If the Facebook security team responded more thoughtfully, we wouldn't even be reading about this as news. Instead of:
"This is not a bug" (essentially, "go away")
...they could have said:
"Thanks for the report. It seems that English may not be your first language, so to be very clear, in order to check this issue, we will need these pieces of information (A, B, C). Please feel free to reply in your language, and we will have a native speaker help translate."
If I was the researcher, the callous "go away" response would have convinced me that it would be more fruitful to sell the exploit to a spammer (who would pay HANDSOMELY to be able to post to anyone's wall).