I'd apply the same principles if it's a start-up or an established company: The nature of the job, work environment, wages, benefits, etc.

What I would take away from the lecture is not to weed yourself out of the market because you perceive yourself to be mediocre. Instead, I'd consider what common threads seem to run among companies that perceive themselves to be start-ups and decide if you'd enjoy working in that kind of environment. Note in particular the comment that start-up founders tend to be terrible managers.

Also, "startup" is a buzzword, and any small company could call itself one. This is another reason to carefully consider the particulars of each situation.