5 and 6 are mutually exclusive. They don't make sense logically. And most of the list was never explained at all.
In practice such situations can arise in one of two cases:
1. some non-sense creeped in
2. logic is applied to a self-contradictory set of axioms and definitions.
(1) is not very interesting, but (2) happens frequently enough because people often do not try to formalize their definitions and axioms. As a consequence they are using some vague concepts and their statements are true in some cases but not in others.
With all that said, I can propose the way how this logical non-sense could be right. (NB. I don't know if it applies to TCP, I'm just thinking generally, and just as an example to all that abstract words above) The notion of "existence" of the mistaken programmer can be wrong. If we accept their definition of existence, then TCP packets doesn't exist, but they exist in some other sense.
Either way, this stuck out to me because usually these type of lists have very simple, understandable statements that just happen to surprise some people by not being true; in this case, the statements themselves are confusing, so I can't really say for certain whether I believe them or not because I don't even know what truth they're asserting to try to negate it.
I would classify these statements as koans, and further observe that one of the defining characteristics of these lists is that they are wry. With that in mind the couplet is evidently presented in cheek to illustrate the need for context, since this is the pathway to resolve the overt contradiction without getting stuck in a rigid thinking trap.