It is still a choice to get angry though. Or are you trying to claim that genetic precursors evolved to feel angry at the question of free will and feelings? And that your post is intentionally created to cause anger?
It is safe to assume that genetic precursors haven't evolved away the choice of response to your post since not every, including yourself, is angry over the topic and we are all genetically similar. It is also safe to assume that your post isn't designed to intentionally cause anger as not everyone has responded the same and doing so would basically be trolling and against the rules.
There is a definitive answer you just are of the opinion to not believe it. If every response is the same then there is no free will. If any response or reaction differs then there is a free will since something cause someone to react or respond differently. What is that concept if not "free will"?