Why was this image rejected for "Grain/Noise Problems"?

[#1]

Once again, and this isn't the first time nor will it probably be the last time, the attached image was rejected for "Grain/Noise Problem". The only way I can see any "grain" is if I magnify the image to over 300%. Then I start seeing the individual pixels which is not grain. The image was shot with a Nikon D7500 using an 80-140mm zoom set to 50mm. ISO was 200; shutter 1/60 and f stop at f18. Other images shot at the same settings and in the same session were accepted without issue. Someone please explain this to me. I don't have this issue with images at Shutterstock or iStock.

(Original image size was 2479x3469 and did not have the watermark.)

[#2]

Once again, and this isn't the first time nor will it probably be the last time, the attached image was rejected for "Grain/Noise Problem". The only way I can see any "grain" is if I magnify the image to over 300%. Then I start seeing the individual pixels which is not grain. The image was shot with a Nikon D7500 using an 80-140mm zoom set to 50mm. ISO was 200; shutter 1/60 and f stop at f18. Other images shot at the same settings and in the same session were accepted without issue. Someone please explain this to me. I don't have this issue with images at Shutterstock or iStock.

(Original image size was 2479x3469 and did not have the watermark.)

[#3 · Accepted solution]

Maybe because of this:

Enlarged to 185% You can see some signs of noise. Adobe tends to be picky.

[#4]

All the shadows have some noise both in luminance and colour.

Additionally, I would expect the picture to be crisp sharp. But it is not. Sharpening helps...but introduces more noise. An aperture of 18 does probably not help.

And not to le a to bad impression: A great subject and a nice framing, great colours.

[#5]

Why would using a small aperture such as f18 introduce "noise" or an "artifact" problem?

[#6]

Unfortunately, I misstated the reason for the rejection: The image was rejected due to 'Artifacts'.

[#7]

The noise includes artifacts, so my above reason is still relevant. Using a small aperture dosen't increase noise, but exposure of the image including ISO does. (The higher the ISO, the more noticeable the noise gets.)

Noise includes both colour and luminance.

Quality and technical issues rejected at Adobe Stock