Jackson Arnold hit the Transfer Portal on December 4, two days after the Oklahoma Sooners hired Ben Arbuckle away from the Wazzu Cougars. Arnold and Arbuckle spoke during that time, and clearly, the conversation led to a swift decision.
There's a 99.99999999% chance John Mateer's eventual landing in Norman was brought up. Arnold made a business decision after that, knowing that he'd be behind in the Sooners' QB battle, and/or that he wouldn't have the same NIL offer coming his way from OU's boosters.
At that point, Mateer was a hot portal name despite having not entered yet.