Chapter 21 of the Dhammapada is titled Miscellaneous or Varied Verses or similar depending on the exact translation. Why do all the other chapters have descriptive headings and themes such as Flowers and Chapter 21 just has this generic title and generic theme?
I can only speculate. If we examine the preceding & proceeding chapters:
Maggavagga is about the Path and verses 273, 274, 275, 276, 277, 278, 279, 280, 281, 282, 285 and 289 all include the word "the path", while verses 283, 286, 287 & 288 are about when the path is not practised.
Nirayavagga is about Hell and every verse is related to the chapter title of hell.
As for the Pakinnakavagga: Miscellaneous, I would classify its verses as follows:
Verses 290 to 295 appear related to each other, which appear to be about higher happiness and freedom from cankers, unwholesomeness & suffering.
Verses 296 to 301 appear to be about another collection of related general practices.
Verses 302 appears to be about a separate topic of certain unique difficulties & sufferings.
Verses 303 to 305 appear to be related to the fruits of virtue.
In conclusion, at least unlike the preceding & proceeding chapters, it appears there are four different categories of teachings in the Pakinnakavagga; thus it is called Miscellaneous.
While I do not know the Dhammapada very well, similarly, I always wondered why verses 153 and 154 were included in the Jaravagga about Old Age.
As Ruben2020 said, often sutta titles are not directly related to the sutta subject matter. For example, the 2nd sermon (SN 22.59) is called Anatta-Lakkhana Sutta yet the word "lakkhana" is not found in the sutta or in any related sutta. While the term "Three-Characteristics" is inherently used in Buddhist discussion, this term actually never exists in the suttas. Based in AN 3.136, the "Three-Characteristics" should probably be called the "Three Natural Lawful Elements" (dhammaniyāmatā sā dhātu) or similar.
The Dhammapada was organized by the monks within a few centuries after the Buddha's passing away. They also wrote the commentaries.
There is no mystical or supernatural or significant reason for the naming of the chapters, other than the reason that it was named so because the monks who compiled the Dhammapada decided to use this name.
They probably called it "Miscellaneous" because they put verses into it that did not fit into other themed chapters.
I do not have credible historical sources to back this claim.
My person thought maybe also give another smart opinion one could buy in, but then thought maybe just tell that it would be good to have a "Miscellaneous" tag for questions...
In those who leave undone what should indeed be done but do what should not be done, who are conceited and unmindful, moral intoxicants increase....
...helps to gain some heartwood from the answer.
[Note that this isn't given for stacks, exchange, other world-binding entertainments but for release from this wheel]