I know this must still keep you up at night, even a year down the line:
The first reference to Ravenclaw occurred in Chapter 3, actually, when McGonagall characterizes Harry's family tradition of exploring bookstores as
the most Ravenclaw thing I have ever heard.
Harry may be unfamiliar with the adjective, but knows it a characterization for his interest in books, or perhaps his faith to family tradition. In any case, Harry already knows Ravenclaw is a house by Chapter 4 as evident through his conversation with Draco:
Harry grinned sheepishly. "Professor McGonagall says that I'm the most Ravenclaw person she's ever seen or heard tell of in legend...
It is reasonable to assume from this reference that McGonagall had discussed the housing system with Harry at some point in between the two chapters, though not explicitly detailed.
I know this must still keep you up at night, even a year down the line:
The first reference to Ravenclaw occurred in Chapter 3, actually, when McGonagall characterizes Harry's family tradition of exploring bookstores as
Harry may be unfamiliar with the adjective, but knows it a characterization for his interest in books, or perhaps his faith to family tradition. In any case, Harry already knows Ravenclaw is a house by Chapter 4 as evident through his conversation with Draco:
It is reasonable to assume from this reference that McGonagall had discussed the housing system with Harry at some point in between the two chapters, though not explicitly detailed.