Yes, when the diode goes off, the diode voltage suddenly collapses from abotu 0.7v to zero, and its klind oif liek a step input, and the buick inductor then rings in the loop comprising the output capacitor and diode, as well as through the output cap and the input source capacitance.
Your question is a regular one on all forums.....most askers are asking how to snub it out because they fear EMC...but it should not be snubbed.