That is a Le Creuset Enameled Cast Iron grill pan. Meaning it is Enameled on the inside as well as the outside.
Treating it like seasoned raw cast iron is going to destroy the enamel finish. The author of this guide needs to go to the Le Creuset website and look up how to care for their products correctly.
In fact, the entire article should be retracted before someone follows your advice.
The article still seems to confuse the two different types of cast iron cookware and how to clean them. Enameled cast iron should be washed with dish soap and water, baking soda may be added if necessary. It can be washed in the dishwasher and it doesn't require seasoning.
Please read the pamphlet that came with your cookware, or the care guide on the official website.