It sounds to me like he was a part of this process from the get-go, with the other creatives behind the show making sure Stewart was as involved as possible as they put the Picard series together.
Stewart also called the opportunity “an unexpected but delightful surprise” and noted that he was eager to work with the “brilliant creative team” that was looking to put together “fresh, unexpected and pertinent” stories.
In fact, when Patrick Stewart officially announced that he was on board for a Jean-Luc Picard series, he noted how “excited and invigorated” he was to be able to take up the character again after so long, and believing that his time in the world of Star Trek was over.