I inferred from the comment that Reddit posters are mostly young men, not that groups predominately composed of young women don't exhibit group think.

I'm not a Reddit user but a quick Google search confirms the ratio of males to females on Reddit is at least 2:1 and possibly 3:1.

There are also various other phenomena that suggest Reddit users of any gender or interest might see a disproportionate number of male posters, but we needn't go near those treacherous waters given the above numbers.