In artery blood flows with a pressure. When part of thrombus detaches it should flow along with the flow but it flows is retrograde manner.
I think you might be talking about Propagation of arterial thrombi.
Propagation is the increasing size of a thrombus and it occurs towards the heart, this is because thrombi are formed differently in veins vs arteries. In veins they form through the accumulation of fibrin and red blood cells whilst in arteries they form through the clumping of platelets.
Embolization is when the clot is removed from the circulatory wall and at this point it moves along with blood flow in both veins and arteries.