It's like the sum of the current at the inverting side is zero, Draw the arrows in the same direction (toward or away from the dot) for positive. No current flows into the inverting input.
So, some I generated by the photodiode is counter balanced by the same current in the opposite direction =I*Rf to make that node 0V.
The OP amp holds it at the value of the positive input. Since OP amps aren't ideal, it holds it at Vos. Vos is a strong function of temperature.
the transfer function is more like Vout = V(non-inverting) - I*Rf; but V(non-inverting) is zero.