Quasi-derivation occurs when two words look or sound as if they were derivatives but do not actually share the required derivational lineage. The example qāla/al-qālīn displays audible likeness despite different senses and lexical analysis.
The rhetorical effect comes from the impression of relatedness. Close lexical study then distinguishes appearance from genuine morphology.
Calling every resemblance “derivation” would erase the distinction between jinās and quasi-derivation.