Likely they look at everything, not just the graded portions, to come up with that kind of split. So if you got 100% on every quiz the first time, every homework and test you'd be in that group. If you flubbed the quizzes here and there, probably not.
They will also probably look closely at that optional programming assignment as well.
I knew there was a reason Google let Peter Norvig take the time to do this ;)