Photodiode connected in reverse?
If you understand the op-amp, you will see that the photodiode has zero volts across it.  It is the functional equivalent of the circuit of Figure 6A in https://physlab.lums.edu.pk/images/1/10/Photodiode_circuit.pdf, shown below.  

Since there is zero volts across the diode, it doesn't really make a difference which direction it points -- the only difference is whether the output generated by the op amp will be positive or negative.  Also, there are some ramifications of not using the photodiode in a reverse bias -- it will be slower, and it will have less dark current.



Note that with the voltage across the diode fixed, you are moving up and down the negative y-axis in this graph, changing current as the light on the photodiode changes.