I dunno how people make up words.
For me, it is usually due to a typo, or some weird thought that popped to mind.
You may be able to contribute. Apparently it is an art. You have a gift!
http://www.nonsensicon.com/
Also in case you are interested:
Nonsense Word Fluency is given in Winter (optional) and Spring of Kindergarten, and Fall, Winter, and Spring of First Grade.
(You might have already missed the fluency test though. ;))