Corn sugar is dextrose, table sugar is sucrose, but they actually ferment very similarly. I think most people consider them to be almost interchangeable in this context. The warning against using sugar in brewing is because many of the cheaper kit manufacturers add a kilo of sugar to their recipes to save on costs. That is rarely a good thing to do. That said, corn sugar/table sugar is used in many different styles and can help a beer to dry out a little bit.
Cream ales are typically mashed with corn, which provides much the same thing that a pound of sugar in an extract batch will. Here, the sugar is appropriate to style. I can't comment on that recipe specifically, but it looks more or less what a cream ale recipe should look like.
It's a good lawnmower beer. Cream ales are a good way to get your corona drinking friends into styles a bit more complicated. Good luck!