Thanks for everyone on both sides for your thoughts.
As several of you noted, while the root cause was not getting the reserved room type, the thing that ruffled my feathers was the FDA's tone and word choice to condescendingly call me a liar. "Oops, I'm sorry..."/"Half our rooms flooded and this is the best we can do..." (perhaps with something else small to make up for it) would have gone a long way.
I'm not going to pull the Diamond Desk into it (I'm not looking for points, etc.; an apology would be nice) but I did drop a short note to the GM that this may be a learning opportunity re: how guests may perceive language and tone.