Slavic krava (cow) had it's name because of the "horns",Latin cervus(deer) because of the "horns",Celtic karwos(deer,stag) Greek kerawos(horned),Greek keras(horn),Latin cornu(horn) Slavic srna(deer) but satemized compare Sanskrit srnga(horn) and so on.. all from common IE root denoting horns or top,head.
For example Lithunian arklys(horse) had a sence "to plough".
You also have other Slavic words denoting horse or a stallion.
For "without horns" compare ancient Greek kemas(young deer) Old Prussian camstian (“sheep”) and camnet (“horse”),Sanskrit sama(hornless),if reconstructed Slavic will be "komnь" or "komon" then it developed into "kon" i personally see nothing weird in it,major difference in the words above are suffixes cause different languages,root is the same.
In the sense with horns or without horns people needed to distinguish them,that's creativity to me,what word would you expect?