catholichierarchy.org is just run by a layman, Terry Boyle. It isn't an official register of Catholic bishops, despite its thoroughness.
I get it, but he has to be relying on some official data source. There's too much data there to be attributable to Google searches, including consecrators, co-consecrators, exact dates of ordinations and consecrations, etc. I'm guessing he's tapped into some Vatican database that he accesses and builds out the HTML from.
Even if this bishop had originally been clandestinely ordained and latter accepted, they do (like Kalata) then show up on the list. I'm a bit perplexed about an Italian being clandestinely consecrated. That tended to happen in Communist territory.
Bishop Thuc also had a similar papal mandate to clandestinely consecrate when needed. In those cases, there is actual PRIOR papal approval, except that it's not made public until the bishop is able to safely come out of the shadows.