The Summerset patch notes claim that Psijic Portals may include motifs from the zone they are found in. However, after farming many and getting quite a few pages of both Psijic and Sapirch motifs, I can quite reliably say that Psijic Portals in Summerset do not include the Pyandonean motif in their loot pool (that, or it has an extremely lower drop rate compared to the others).
I could also find no one online stating to have gotten any Pyandonean from the portals.

With the Pyandonean motif being made available ingame at a later point in the Summerset PTS cycle I'm not that surprised if it had been "forgotten" to adjust the portals loot pool to include it.