Mice are far from perfect proxies for humans, but when it comes to dietary and nutrition studies, they are surprisingly good matches. Others have pointed out the cost/quantity/ease advantages of working with mice. Another big advantage is that some mice (and many rats) are opportunistic omnivores, like humans. As such, their digestive systems have evolved to be reasonably similar to ours. (Key word here being "reasonably").

Can't claim to know personally but a quick search turns up numerous results claiming that mice and rats are similar to humans in anatomy, genetics, internal processes, etc. I think they become even better candidates when you compare them to other possible test subjects, especially factoring in the cost/value. They are relatively cheap and easy to breed with almost no genetic variation (good for testing), accelerated lifespans, small, etc.

Did you even read the article?

> the scientists found that feeding Neu5Gc to mice engineered to be deficient in the sugar (like humans) significantly promoted spontaneous cancers