From the article: "concentration of sugar in the sucrose solution was the same as is found in some commercial soft drinks, while the high-fructose corn syrup solution was half as concentrated as most sodas" - meaning they weren't actually trying to compare Sugar vs HFCS. Since they weren't offering the rats similar amounts of each. So, did the rats gain weight because they preferred the less sweet HFCS solution and thus drank more?
From the article: "Animals with access to high-fructose corn syrup gained 48 percent more weight than those eating a normal diet" - meaning the second study wasn't even comparing Sugar vs HFCS - just HFCS vs nothing. Of course rats who ate a bunch of HFCS were less healthy than those eating relatively lean and low-sugar rat food.
Neither of these studies attempts to compare between equivalent consumption of Suger vs HFCS. And if you read the actual study, you will see that they did not intend to. That's not to say that HFCS is perfectly safe - but this study does nothing to study "equal amounts of sucrose and HFCS in a human metabolism" - or any other animal's metabolism for that matter.