I took a photo of San Francisco Bay using a Kodak Easyshare digital camera in 2007. The photo came out with the grass in the foreground being green and the entire remainder of the photo (the bay, Alcatraz prison and the sky) came out in black and white. How can this happen when the camera was only capable of taking color photos? I took the photo on an overcast day. I took thousands of photos using that camera and that is the only photo that ever came out that way.
At least the later Easyshare cameras had a feature called "spot color": it would allow you to select a color, and the rest of the picture is converted to black and white.
I was able to find this feature described for an Easyshare camera introduced in 2011 (it says: "[...] or add in effects like background blur and spot color easily from the touch screen."). Not sure if your camera had a touch screen, but you might have accidentally enabled the effect for the one specific picture, causing the effect you describe.