At KDE bugtracker https://bugs.kde.org/show_bug.cgi?id=361491#c15 it has been recognized that icons 'aggregation' and 'composition' looks to be swapped. The UML standard defines the icon for association type 'composition' as arrow with a filled diamond at the top (for example at http://www.uml-diagrams.org/composition.html?context=class-diagrams) while icons for 'aggregation' are defined as arrow with empty diamond at the top (see http://www.uml-diagrams.org/class-reference.html)
In the breeze icon set the 'aggregation' icon is defined with a gray filled diamond (see https://quickgit.kde.org/?p=breeze-icons.git&a=blob&h=099a91c9b960300ffebe548f81893db5b560f5b0&f=icons%2Factions%2F22%2Faggregation.svg&o=plain) while the 'composition' icon is defined with an empty diamond (see https://quickgit.kde.org/?p=breeze-icons.git&a=blob&h=d9de62931fde8a5be80d1833456471e099b9879c&f=icons%2Factions%2F22%2Fcomposition.svg&o=plain)