Processed 4 rolls of film, one has a green tint?

[Rudeofus]

He meant when he pulled the rewind knob it may have been that the back popped open slightly and as he was rewinding the film it passed through the area with the "light leak".

Not sure if that makes sense but I'm really at a loss for what it could have been.

This makes a lot of sense, for two reasons:

1. Film has an anti halation layer, which prevents scattering of light and thereby protects areas surrounding strongly exposed area (look for Cinestill 800 images with light sources in the image frame: that's what you get without anti halation layer). Anyway, this anti halation layer also prevents light passing through layers of film tightly wound on a spindle, and people who accidentally opened the camera back for a very short time reported that only a few frames were lost to fogging. The error you describe would expose/fog all the film - which matches exactly the phenomenon you reported.
2. With the camera back only slightly open, your friend gave the film a strong exposure (it's ISO 400 film after all), but not strong enough to obliterate all image detail. The green color would be the complementary color of tungsten light.

 

[AgX]

He meant when he pulled the rewind knob it may have been that the back popped open slightly and as he was rewinding the film it passed through the area with the "light leak".

Thank you for that explanation! Yes, that really makes sense, especially on fogging the complete film.
I did not relate that crank pulling with that door opening.

I've been a fool. As usual...