really need to know if this is manipulation???

So my exn is acting very somber. No emotion, actually doing what I asked as far as our son is concerned. But he acts robotic. We only talk over e mail but he says thing's like as you wish when I say something. He's been agreeing with everything suddenly with no anger or emotion period. I recently told him I wasnt interested in him and was moving on. Now his behavior is so strange? ? I need advice! Thanks!