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.
Yes. If one applies correctly the rules of logic on inconsistent axioms, the conclusions will be inconsistent. If one incorrectly applies logic to inconsistent axioms, the conclusions may or may not be consistent. It happens IRL sometimes; "being right for the wrong reasons".
That being said, I suspect the game of the author is to play with leaky abstractions. TCP is a stream-oriented protocol, but is implemented on top of frames etc.
The point is that a lot of stuff in Networking (and Computer Engineering in general) is very context dependent, and that you cannot be extremely opinionated about this stuff.
They are not mutually exclusive statements, because they don't exist in isolation: they are both potentially true and false depending on the context of discussion.
This seems like it's either a linguistic or philosophical question; either I don't interpret the words "such a thing" in a way that the author meant it, or I have a divergent different philosophical worldview on the concept of "existence" from the author's own view.
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.
> these type of lists have very simple, understandable statements
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.
But they assert whether or not something exists, as an absolute statement. Maybe TCP packets don't exist in a particular situation, but there is still such a thing as a TCP packet in that case.
