Back at the apartment there is little doubt that Jallah knew he had it (she said she was learning about symptoms on TV). She probably told her kids not to touch. The other thing is that every patient is different in the amounts of virus they will shed given various symptoms. IOW, even if Duncan were vomiting a lot, it doesn't mean he was shedding a lot of virus in the vomit. He may have vomited into pillows and kept it from splashing around. There are many unknowable factors.
Just as the news comes out that the incubation period may actually be 40+ days for about 5% of the people exposed.