First, it's about attention to detail. Have a good look online of various darlington pair h-bridge circuits, and notice that the left-side of the circuit will have an npn darlington pair and a pnp darlington pair. That is...two different types of transistors on the left-hand side. The same case will apply to the right-hand-side of the circuit.
Now take a look at the circuit that you showed...... and look at the left-hand side. Does that look like two different types of transistors? Or does it look like the same type?