That diagram is rather bad at what it tries to do. Those are also historically and phonetically the same: Λ Л Δ Д Κ К The first Cyrillic alphabet was using the https://en.wikipedia.org/wiki/Glagolitic_script , curiously created by Saint Cyril, but then people found it was too difficult, so someone in the Preslav Literary School in the First Bulgarian Empire mashed up Glagolitic, Greek and Latin to create the new Cyrillic (probably naming it as a sorry to Cyril for butchering his nice unique alphabet).