He was already working for Apple before moving teams internally, probably because his DTS job wasn't working out or the perks of switching were too great, i.e.

He was already working for Apple before moving teams internally, probably because his DTS job wasn't working out or the perks of switching were too great, i.e. he started at DTS a year ago, and before that year was up he switched teams and then presumably quit altogether. He wasn't hired by Apple expressly to come impart his wisdom onto the team working on the app.