I have found the same thing happen at Google images, not just TinEye.
At times, the image is not found at Google, but found at TinEye and visa versa. I use both sometimes to see if there are different results.
Keep in mind, some people who make their websites block crawlers from indexing their images on purpose, to stop others from stealing their images.
It could happen that TinEye was blocked from indexing the image(s) but not Google. Either way, never depend on Google or TinEye 100% to locate or match an image, ... yet both provide excellent image search tools.