If you can confirm that Quick Cache created it, then I will be able to confirm that nothing else will be using it :-)
Yes, Quick Cache creates the
wp-content/cache/ directory, but there are other plugins out there that also create that directory (usually only other caching plugins, so if you don't have any other caching plugins installed, it's probably safe to assume that Quick Cache created it).
In any case, if you don't see anything inside the
wp-content/cache/ directory except for a
quick-cache directory, then yes, Quick Cache most likely created it and you're safe to delete it after uninstalling Quick Cache.
Note that this has already been fixed in the latest development trunk and will go out with the next release. https://github.com/websharks/quick-cache/issues/261