Hi mahacrown,
They are actually considering whole CaI2 compound as the "solute." Generally, the question should be more clear when talking about solutes but the AAMC decided to be vague with this question. They should specify "moles of ion X" to be more clear.
Based on this, the answer should be 650 mL as you have found.
When you read the question and it is referring to "the" solute, as in just one solute, it probably is safe to assume they are referring to the original compound as a whole.