"That guy" (tchrist) is a moderator (as you can tell from the little diamond thingy, ♦ , after his name) and he deleted your post because it fell afoul of our attribution requirements as noted on our "Referencing" help page, at https://english.stackexchange.com/help/referencing (under "Help > Help Center : Answering > How to reference material written by others"):
How to reference material written by others
Plagiarism - posting the work of others with no indication that it is not your own - is frowned on by our community, and may result in your answer being down-voted or deleted.
When you find a useful resource that can help answer a question (from another site or in an answer on English Language & Usage Stack Exchange) make sure you do all of the following:
- Provide a link to the original page or answer
- Quote only the relevant portion
- Provide the name of the original author
There is additional material on proper attribution form at "New attribution rules" and its top answer.
The short answer, though, is that an improperly attributed answer may be subject to immediate deletion regardless of its other redeeming qualities. I am sorry you ran afoul of this requirement, but there it is.
As to the nature of the comment he left, I can only say that reading tone into a text-only comment is fraught with opportunities for insertion of ill will where none was meant. Yes, it was a bit terse, but I don't believe it was intended to be rude or accusatory; rather it was a (brief) explanation of why he felt deletion was justified ("it's a duplicate and it lacks the attribution we require").
I apologize if you feel you were robbed of your agency in determining how to manage your own post. However, if your response would have been to delete it, that has been taken care of. If you believe you could have expanded it and added attribution to make it more comprehensive and useful than the other post which also mentioned the same word, you are still free to post a new version of your answer with the enhancements.
(Also, just for reference, you can find the complete list of moderators by selecting the "Users" link under the site header, and then choosing the "moderators" tab (all the way to the right)., which will take you to this page.)