ACF does not crate “responsive imaages”, it just stores and image ID and returns what you ask it to return, array, url or id (url will always return the url of the full size image), it us up to us to do what we want with these values to display images as we want them to be displayed.
If you have an image that is 1000×1000 that is a 1:1 ratio. If you have not other image sizes that are a 1:1 ration then no other image sizes will be added to the src set. However, the default image sizes added in WP are all 1:1 ratio image sizes and they will be added if you do not alter them.
srcset and @media are two different subjects. The first is an attribute of an <img> tag and the other is done in CSS and usually to set a background image.
