The rect is at position (200, 0) inside the item's coordinate system, but the item itself is at (0,0) in its parent's coordinate system.
The QGraphicsScene::addRect() documentation explains this:
Note that the item's geometry is provided in item coordinates, and its position is initialized to (0, 0). For example, if a QRect(50, 50, 100, 100) is added, its top-left corner will be at (50, 50) relative to the origin in the items coordinate system.
Alternatively, you can add a rectangle at 0, 0, 5, 5) and move the item afterwards, to get the result you expected:
QGraphicsRectItem* r1 = addRect(0, 0, 5, 5);
r1->setPos(200, 0);