Clone Layer Has Color Cast

In the attached screenshot, a student ofm ine has retouched on a layer using the Clone Stamp and the Spot Healing brush. He did so after using a Levels adjustment layer. I checked his settings, the Blend mode in the tool options bar at the top of the monitor is set to normal. Protect tones was off. I tried replicating his set up on my end and got the expected clone layer without the blue cast seen in the screenshot below.

Any ideas as to what is causing this color cast from the clone stamp?

Thank you.