A word's multiple senses are not sufficient by themselves. An unintended sense must suggest an apt relationship with another expression nearby. Without that contextual relationship there is no clear instance of apparent congruity.
This should not simply be equated with tawriyah. Tawriyah focuses on the interplay of a near and a remote sense and which one is meant; īhām al-tanāsub focuses on the resemblance that an unintended sense seems to create with surrounding words.
In the najm example, interpreting the word as a star would mistake an association generated by the context for the verse's intended botanical meaning.