Docker Image for specific CPU Architecture

Hi
Im new to building docker images and have run into a problem.

I have a base image from alpine from which I have built an image for a raspberry pi zero. The image runs fine.

I pushed it to a local repo and when I pull it again and run it on another zero, I get an error message saying that the amd64 arch does not mach the arm one. But the image still runs.

I am not sure what is happening here, I would have thought that given the alpine image is for arm32v6 that the image should be as well. Also I did not get the error message until I pushed the image to the local repo and then re-pulled it.

My question is, how do you flag an image to be for a specific architecture such as arm32v6 in my case, is there a flag I have to set or something.

I have searched but cannot find anything relevant to my question, most answers on google are to do with multi-arch files.

thanks

jack