I suspect he's talking about spam e-mails featuring links to porn websites. Those spam e-mails are not the fault of the receiver. Porn sites buy e-mail lists which are culled from any number of legitimate sources (postings on regular non-porn Usenet newsgroups or online subscription newspapers for instance). Then they send their spam. I've never visited a porn site in my life yet I get porn spam. I delete it immediately, no problem.
Excellent point. JimRob even points that out on your profile page: "Be aware, the given e-mail address may be indexed by third-party spiders. If you supply your e-mail address, you may be subjecting yourself to spam. This is beyond our control, and it is a common concern shared by many on the Internet."
Damned spiders are everywhere.