As the author mentions in the article, platinum may not be cheap at the moment but it certainly appears to be undervalued vs Gold
Here's an excerpt from his article.
Since 1972, Platinum traded at about 1.35 times the price of Gold on average. Right now, Platinum is even cheaper than gold, trading at only 0.92 times the price of Gold. As we can see in the chart below, this is a rather “rare” situation. It only happened in the early 80′s and for a short time in 1974. In 1972, 2000 and 2008, it even traded as much as 2.30 times the price of Gold (monthly basis).