Ahsoka Finale Spoilers - Tumblr Posts
He was so busy worrying about Ahsoka and avoiding a direct confrontation with her that he forgot to worry about Ezra.
Or he made the assumption that if Ezra or Sabine managed to get onboard they would have immediately sought him out and tried to wreck stuff or announced their presence somehow.
Thrawn thinks he got back to the proper galaxy undetected. He thinks Ahsoka, Sabine, etc. are all stranded (true for the most part) and can’t warn anyone of his return.
He has no idea Ezra got on board his ship. He doesn’t know Ezra made it to the New Republic and is able to warn them, ruining Thrawn’s element of surprise. Ezra might even be able to tell the New Republic that Thrawn went to Dathomir.
Once more, Ezra Bridger is going to fuck up all of Thrawn’s plans.