Your code isn’t selecting for events only in your Bodypoly, but rather is accepting the mouse click from anywhere.
Utilize the CollisionObject2d signal “_onArea2D_input_event” in the Area2D node by connecting it in the editor to your Bodypoly node and override the function like this:
func _on_Area2D_input_event( viewport, event, shape_idx ):
if event is InputEventMouseButton:
if event.get_button_index() == BUTTON_LEFT and event.is_pressed():
get_node("AnimationPlayer").play("change1")