How does Bigger compare his home to the Dalton's in regards to the smell of food?

Let's take a close look at the exact passage you're referring to in Richard Wright's novel Native Son (1940).
To set the scene, Bigger Thomas is the protagonist: he's a twenty-year-old African American boy living in a poor area of Chicago in the 1930s. Early in the novel, Bigger takes a job as a chauffeur for a rich white family, the Daltons. His first task is to drive Mary Dalton, daughter of Mr. Dalton (a real estate magnate) to a lecture. The evening doesn't go as planned: Bigger has a friendly dinner with Mary and her friend Jan, and the three get drunk. Later, in a confusing moment back at the Dalton home, Bigger accidentally kills Mary (this is hard to summarize in a sentence, but essentially he holds a pillow over her face to stop her from speaking when her blind mother comes into the bedroom, smelling alcohol; and he accidentally suffocates her).
In this moment of the narrative, Bigger has woken up the next morning, remembering the terrible events of the night before:

Gus and G.H. and Jack seemed far away to Bigger now, in another life, and all because he had been in Dalton's home for a few hours and had killed a white girl. He looked round the room, seeing it for the first time. There was no rug on the floor and the plastering on the walls and ceiling hung loose in many places. There were two worn iron beds, four chairs, an old dresser, and a drop-leaf table on which they ate. This was much different from Dalton's home. Here all slept in one room; there he would have a room for himself alone. He smelt food cooking and remembered that one could not smell food cooking in Dalton's home; pots could not be heard rattling all over the house. Each person lived in one room and had a little world of his own. He hated this room and all the people in it, including himself. Why did he and his folk have to live like this? What had they ever done? Perhaps they had not done anything. Maybe they had to live this way precisely because none of them in all their lives had ever done anything, right or wrong, that mattered much.

So, to your question about the smell of food and what it says or doesn't say about the Thomas home versus the Dalton home. At the Dalton home, there is never a smell of food (all of the cooking is done behind closed doors in the kitchen of the large home) and there is plenty of space (everyone has his or her own bedroom to retreat to). At the Thomas home, in contrast, everyone lives on top of each other, and the smells associated with the preparation of food are nearly constant.
This observation about the smell of food illustrates the contrast between Bigger's poor background and the world he aspires to be a part of—and the sorrowful realization that now, especially, remembering the crime he accidentally committed the night before, that Bigger will never be able to join.