They are saying it might have arrived during the Military World Games that was held on 18 Oct 2019 in Wuhan.
Either as competing participants, foreign officials or foreign spectators.
As shortly after that (during November), Chinese residents in Wuhan started getting sick.
Of course, this is just speculation from the China side - the Italian will need to trace all the people that Italian boy came into contact with and find out whether any of the close contacts attended the games.
It might take another 6 months to a year to find the original source, but they are getting closer.
