Surely you can see how this could cause problems for someone else who has the bad fortune of taking your advice at face value.
Cut to John Doe. John is the son of Mr Doe, who owns a law firm. He spends time off working at his dad's law firm, because he intends to become a lawyer. John is not paid.
If I am told to cease and decease by a lawyer/my school/a policeman - no deal, I'll just stop and say: gee, I was in it because I wanted to learn stuff. Out of my own free will. I can't? No problem - I'll just stop. Ditto for John (though for some reason, I doubt anybody'd actually punish John, or even Mr Doe).
I don't see how I'd get in trouble. His article is directed at the non-technical student, not the employer. (If it was written for an employer/startup founder, then perhaps you're right to suggest that he should disclose that he's giving law-breaking advice. I'd be fully behind you on that one, qeorge, I would.)
But the article's fine as it is. And there's a corollary, of course. Entrepreneurs are relentlessly resourceful. If you're not relentlessly resourceful in figuring out a way to get into a startup for the experience, then you're probably not going to make it anyway.
It's an article that belongs on the founder's personal blog, not the company's blog.