It would indeed be great news if the rate of infection were decreasing, but I'm a bit puzzled.
Firstly, how do researchers know? Many people with mild symptoms are just staying at home and not seeking medical help.
Secondly, this is only about people from 20-69. Experience in other countries shows that the vast majority of serious cases have been amongst those over 70. There are various reports about infection rates in care homes, all of which are high.
I'm afraid I'm taking this with a large pinch of salt.