The hyena and the hound are sworn enemies. The dog, being man’s best friend, assists the man to hunt and chases away hyenas that will want to scavenge on the same prey. Hyena’s look at dogs in amazement at their obedience to man instead of joining their scavenging ways. Dogs do not fear hyenas and hyenas do not easily run away from dogs - hence the direct confrontation is vicious. Dogs have been torn apart by hyenas where they were not skilled in hunting or outnumbered. Hence it is highly unlikely that dogs would ever be seen playing with hyenas - it would be quite an astonishment. Our elders observed this in human traits and likened it to the amazement that happens when one finds their enemies getting along with one another.
The proverb is used to question or show amazement of two opposing forces coming together. It is also used as a word of caution to those who may not sense anything wrong with two enemies becoming cordial to one another.