The press release has some things in it that are not true: 

It says: "This virus is known to replicate in the liver, but not known to cause hepatitis and cannot replicate without a 'helper' virus". Everything after the comma is not true. These viruses replicate without a helper and cause hepatitis, but it has only been seen in immunocompromised children. 

It says: "That suggests some children may be genetically more susceptible to some forms of hepatitis". This is not true. What this genetic polymorphism indicates is that the immune response to viral infection may be different in these people. 

The studies in Nature are credible, but the limitations are well put by Tacke [the author of the News & views article accompanying the three studies]. They are retrospective studies. At the moment there is no confirmation in in vitro studies (with organoids, for example, to confirm the potential direct effect of the virus on the hepatocyte), nor prospective studies showing that hepatitis is caused by the interaction between a generally low pathogenic virus with an altered or deficient immune system (both because of the genetic polymorphism and because it is not adequately developed by the measures taken against covid-19).