They also didn't need to decoy sending Yesavage and Gausman to Bullpen in the Yankee series but they choose to anyway. They actually had them go individually and noticeably solo just to put the thought in the Yankees mind.
Maybe leaking that video was put the Mariners minds they don't need to prepare for him. These professional sports teams do these little games all the time. Normally you don't get both picture and audio of a player doing a private workout. You might hear a sports writer say you saw a certain player throwing, hitting, or whatever but that video had like several angles and audio lol.
I could be completely wrong but I am kinda calling bs on it for the time being.