The Portmanteau of Breakfast and Lunch in Paris

Smog is when you look out at the city and you see like a dirty sort of haze over the city, it's a mix of sort of pollution and maybe a bit of fog. Another Portmanteau I discovered was brunch which is a mix of breakfast and lunch. In Paris, they advertise brunch in restaurants and cafes from 11 a.m. to 3 p.m. But how is that a mix of lunch and breakfast? It's just a long lunch with a lot of eggs.