I don't know your french level but perhaps you read your quote too fast because it says: "Mets qui vient après les hors-d'œuvre et AVANT le plat principal".
So the "entrée" is the dish that comes BEFORE the main dish.
>>>> Par extension. Plat principal. Un repas composé d’un hors-d’œuvre, une entrée et un dessert.
"By extension. Main dish. A meal consisting of an appetizer, an entrée and a dessert."
There the "entrée" is clearly the "main dish".