The internal struggle of the undead army could not be hidden from the Undead Overlord. Although a ceasefire agreement had already been reached between the Undead Overlord and the Blood Moon Lord, given their relationship, such an agreement was hardly enough for them to completely ignore this matter.
While on the surface, both Lords seemed to ignore the struggle between Zhou Tian and the undead branches. But in reality, they had always paid close attention to the progress of the war, and it wouldn't be surprising if they already treated this war as their private contest.
As such, upon witnessing the internal struggle within the Undead Army, the Undead Overlord felt utterly humiliated.