The clue is right after the word "demisable":
no components of subsequent iterations of the satellite will survive atmospheric re-entry, reducing casualty risk to zero
This means the satellite components are built to be fragile enough to burn up entirely on reentry. How that's done exactly depends, options include reducing material thickness, the use of materials with a low melting point, fasteners with limited strength to make sure the sat breaks up, etc.
NASA has tools to check if a satellite will burn up on reentry:
NASA maintains two levels of reentry risk assessment software:
DAS (Debris Assessment Software) and
ORSAT (Object Reentry Survival Analysis Tool)
Both software tools require a detailed description of each component comprising the space vehicle in question.
– Material properties, shape, dimensions, aero and thermal masses, and, if applicable, internal construction, e.g., electronics box.