Magica hadn't planned on eating a full meal, but if he was going to make the effort, why not? It also gave the twins another chance to info-dump on Scrooge. Though she definitely didn't mention the "one to watch out for", for obvious reasons.

When they returned and stood in the doorway, the actual implications sunk in. Once again, they cocked their heads with mutual confused looks. A man so rich that millions and billions were nothing to him, and there he was, cooking fried food. He wasn't complaining about it either - rather, he was eager to do menial servant work. It didn't add up.

"He's an odd one."
"That's for sure."