After reviewing the code, I realize that this code was originally reported by @grantat. Using https://www.webarchive.org.uk/wayback/archive/20090522221251/http://blasttheory.co.uk/, we get the following card:

With the original run of MementoEmbed, we used to get this card:

This occurs because the UKWA started using a frame banners. A potential solution is to use one of the other Wayback flags for Wayback sites, like im_.