LULU moves beyond yoga to areas that are most likely to be relevant to its high-end core customer: swimming, cycling and such. And, on its move into cycling, for example, the company mitigates its exposure by not only starting small, but partnering with one of the world's biggest bicycle companies, Specialized, on clothing.
Compare the product lines at LULU, NKE and UA. It's quite obvious that LULU presents a much narrower focus than NKE and UA. Whereas LULU's future trajectory seems clear (concentrated on a handful of highly-targeted lines), NKE and UA tend to serve a wide spectrum of folks, ranging from casual sports fans to hardcore athletes.
As far as the stock goes, of course, it was set to get hammered on any whiff of seemingly bad news. The same thing has happened in the past. Growth stories, even great ones like Lululemon's, simply do not go up in a constantly straight line.