Final answer:
The reader assuming the spell had been cast on Roisa, not on everyone else represents a textual inference.
Step-by-step explanation:
The reader assuming the spell had been cast on Roisa, not on everyone else represents a Textual inference. A textual inference is made when the reader draws conclusions based on information directly stated in the text. In this case, the reader is inferring based on the information presented within the text and making an assumption about who the spell was cast on.