You didn't do anything wrong.
This is how "Wonderful Wikitreer" comments go — here to G2G so others can also join the appreciation.
If you want it to be just between you and the other person, you would need to use the [send private message] link from their profile. If you don't mind others seeing what you say, it can be by way of a profile comment, or this type of G2G appreciation "thread". (No matter what, they always show as a question, even when they are not.)