There seems to be something different about their feed or XML structure.

That is an Atom feed (not an RSS feed) as indicated by the use of a {http://www.w3.org/2005/Atom}feed element for the root.

RSS is a poor spec. It requires guesswork by the reader. Atom is a very similar spec that addresses the issues of RSS. Most feed readers can handle both.

When I run the script below, I get "Found 0 entries".

XPath //entry looks for descendant nodes named entry in the null namespace. Atom feeds contain no such nodes. You need to look for entry nodes in the http://www.w3.org/2005/Atom namespace. See the notes for the findnodes sub. They apply to find as well.

Might I suggest XML::Atom::Syndication::Feed

Update: Added third paragraph.