It was obviously a summary.
Much like the letter to Herodotus or to Pythocles are summaries that cover a wide variety of topics but still hang together as identifiable by theme.
Or another analogy is with the atoms themselves and how in Sedley's words we have to avoid radical atomic reductionist thinking that only the atoms are "real." (Just as Epicurus seems to have opposed that line of thinking in Democritus.)
The individual sentences of the PD do deserve separate and detailed examination, but when they come together in summary they produce a "body" which has real characteristics of its own that are not identifiable when looking only with a magnifying glass -- like the forest that can't be seen if we do nothing but look at leaves.