It was actually mentioned in Finchs comments on our Mage. He was near the end of his early education and was set on a path to the college, and of the branches, illusion stood out to him more. With the college just around the corner, it wouldn't be far fetched for a student to start looking into their intended field.

If that wasn't mentioned in the sheet, I am sorry. Working on a phone, you make shortcuts and forget things.