IIUC the input to LLMs is tokenized not on word boundaries but some kind of inter-syllable boundaries, because then whatever the model associated with "task" will also apply to "tasking", "tasked", "taskmaster", etc for example. So a model making up compounds that don't exist would be fully possible and even desirable, especially since real humans do it with English all the time.

They’re called “lemma”

The intent is the same, but as I understand it LLMs don't tokenize based on lemmas, though some of the tokens probably line up with them.