That isn't an endpoint that this study is able to determine at this point, sadly. The people were not being tested for RNA regularly, only if they became ill or concerned they were infected.
In about six months, we will know better - study participants are being tested for nucleocapsid antibodies every few months. The vaccine does not contain the nucleocapsid protein, so nucleocapsid antibodies (which are utterly irrelevant to infection control) would indicate an actual infection. If they don't get infected they can't spread it - but I will bet you ANYTHING that those who DO get infected are at least less infectious.
It means that they have put out a press release. I would be waiting for the paper and hopefully more data. I have found that such press releases often subtly and unsubtly overstate how good the results are.
From the reports, it looks like 90% of the infections were in the control group. Make of that what you will. It does sound encouraging. We don't know if the "uninfected" were shedding virus at any given time.
From reading the news it's not clear to me whether some of those people who receive the vaccine and are in the 90% where it works will be asymptomatic but still infectious. Does anybody know more?