Filoni should have been a politician. He would take over the world with non answers and double speak of this quality

From the VF article (which was also my guess)

AB: That quest, we learn, is a search for the villain Grand Admiral Thrawn. The last time fans saw Ahsoka was this spring's finale of The Clone Wars, but in the actual Star Wars chronology, the last time we saw her was at the end of Rebels, venturing off with Sabine Wren to find Ezra Bridger, who vanished along with Thrawn. Where does that scene fit in with where we find her in The Mandalorian?

Filoni: Right. But no, it's an interesting one… That's not necessarily chronological. I think the thing that people will most not understand is they want to go in a linear fashion, but as I learned as a kid, nothing in Star Wars really works in a linear fashion. You do [Episodes] Four, Five and Six and then One, Two, and Three. So in the vein of that history, when you look at the epilogue of Rebels you don't really know how much time has passed. So, it's possible that the story I'm telling in The Mandalorian actually takes place prior to that. Possible. I'm saying it's possible...