Drummer Chad Smith on the show: "Cardiff Stadium was a warm up for the 3 Hyde Park shows. James Brown opened. And I think it may be the only time we played Mini Epic live."
The "3 Hyde Park shows" Smith referred to (June 19, 20, and 25, 2004) are represented on the band's first live album, Live in Hyde Park which contains a selection of songs from all three shows. Unlike that album, Cardiff, Wales: 6/23/04 consists of all the songs from a single concert on June 23, 2004. The song selection on the album effectively ignores the group's first four studio albums, in addition to their sixth, and includes tracks only from the band's fifth (Blood Sugar Sex Magik), seventh, and eighth studio albums.
The show features a live version of the unreleased song, "Mini-Epic (Kill for Your Country)", marking the first official (albeit live) release of the song that was originally recorded in the studio during sessions to record bonus tracks for the band's 2003 Greatest Hits album and said to have been intended for an anti-war compilation album that producer Rick Rubin was putting together and that was never made.