I'm having trouble understanding your question in the context of the discussion, so I will talk about the topic generally instead.

Imagine a server allows you to upload images. It has a system designed for images only. It will behave unpredictably maybe even dangerously with another file. The server checks that the file ends with .jpg. it checks that the file is a valid jpeg. All clear. Upload allowed. But 5 steps later some tool looks at the image file and notices it's a valid zip file (creating files with multiple valid interpretations is something people have succeeded in doing it's not always so hard). It runs this check before the image check. The next step in the processing chain wants an image but it has been told it's dealing with a zip file. So it unzips the file to see if it contains an image. But it was a zip bomb. The server goes down.