Ah! I didn't even realize there was a PDF, or that this was an article from Math Horizons. You must be right. That also explains another thing that confused me

Ah! I didn't even realize there was a PDF, or that this was an article from Math Horizons. You must be right. That also explains another thing that confused me: Every time the article mentioned a specific video, it could have easily linked to them, but didn't. The magazine being the source of the article explains that too.