From the story on the ITV site... "We intended to recommend the site for listing at grade II, however this is not confirmation it would have been listed, the Department for Culture Media and Sport is responsible for deciding which sites are designated and at what grade.
– Historic England statement "
(My bold and italics.)
So the building wasn't actually listed, just under consideration for listing. Doesn't make what the developers did right in any way, shape or form though.
ETA that IIRC you need planning permission to demolish a property and the developers didn't have that. The local council might now refuse planning for the proposed development (again) but if the developers appeal (possibly after the land has been sold on [maybe to the directors under a different umbrella...]), they'll probably get the permission now there's no longer any structure on the site, let alone a protected building.