Please explain the meaning of the following sentence in conversation

They must have bused some of them in


Hi, Viola. Anybody sitting here?
B: Oh, hi, Tyler. No, have a seat. Looks like the whole dorm came to have lunch today, doesn't it?
A: Yeah, it does; it's crowded. They must have bused some of them in! Hey, in class today I heard you say that you have a big family.
B: That's right. I've got six brothers and five sisters.
A: Wow! That is pretty big! Are you the oldest?
B: No. Actually, I'm the second oldest.
A: That's got to be a lot of work. What do your parents do?
B: Well, my father drives a cab. He works out at the airport at night.
A: What about your mother; what does she do?
B: My mother runs a small family store.
A: What kind of store is it?
B: Oh, we mostly sell food - bread, eggs, milk, rice, that sort of thing.
A: I guess a food store like that would come in handy if you had a large family.