He was able to bypass the portal process by WITHDRAWING from Purdue in January and enrolling at Notre Dame, a move that is permissible under certain NCAA rules, although it some cases it would require an athlete to pay a buyout to depart.
Other cases are different because the athlete stays enrolled at the school and therefore has to finish out the semester as a student. For example, DJ McKinney is still a Colorado student (via Online) finishing up the semester but is coming to ND and even living in Indiana. Porath is already a ND student as of last week.