.js and .css files appearing in image folders

I'm hoping someone can tell me if it is normal that with hummingbird activated the files inside the image folder (specifically 2017>3) all turn to .js . I see a ton of .js in the folder and if I delete hummingbird they all go away. These .js files are in quite a few of my accounts. Always in the same path. (content > uploads > 2017>3) Is this the way it's supposed to work? Sucuri told me it's some form of minification. I'd like to double check that with others. Thanks for any info