I also didn't know much of the difference between the two, and I also used RSS for my Hugo site.

At the bottom of the article there's, under "See Also", a link to this page comparing RSS and Atom: https://www.intertwingly.net/wiki/pie/Rss20AndAtom10Compared...

It seems like the last update is from 2008, but the section on the differences has a few interesting items. I am not sure if it changed, but it says:

"The RSS 2.0 specification is copyrighted by Harvard University and is frozen. No significant changes can be made (although the specification is under a Creative Commons licence) and it is intended that future work be done under a different name; Atom is one example of such work."

The Wikipedia RSS page has also a small section comparing RSS and Atom: https://en.wikipedia.org/wiki/RSS#RSS_compared_with_Atom

"Technically, Atom has several advantages: less restrictive licensing, IANA-registered MIME type, XML namespace, URI support, RELAX NG support.[35]"