Attack of the Postmen was an adventure recorded and logged by the Doctor's TARDIS. The Thirteenth Doctor watched it while in self-isolation. (PROSE: Press Play)
Behind the scenes[]
This is evidently a reference to TV: Kerblam!, which featured the Kerb!am Men. Both Kerblam! and Press Play were written by Pete McTighe.
Attack of the Postmen is re-titled in the style of "classic" Doctor Who adventures like Attack of the Cybermen, whereas Kerblam! follows contemporary 21st century sensibilities.