I get what you're saying, but its still fair to call it a hashtag, and for them to call it hashtagstartup.
Solid hacker news etiquette there, by the way.
Also, you get what you dish out. Saying its "dumb" is what earned you the 15 year old in me. had you said something like "i disagree with their use of the word hashtag" it would have given an entirely different tone, don't you think?