This must be the explanation as it was near evening when the phenomenon occurred.
Refraction and reflection in a raindrop, producing a rainbow.
Source: english wikipedia, original upload 01. Jan 2003 by en:User:DrBob
Religion and mythology
Picture: Noah's Thanks Offering (c.1803) by Joseph Anton Koch. Noah builds an altar to the Lord after being delivered from the Flood; God sends the rainbow as a sign of his covenant (Genesis 8-9).
Rainbow diagram showing the conventional arrangement of colours: Red Orange Yellow Green Blue and Violet. The colours shown do not necessarily correspond to actual wavelengths.
A vectorized version of Rainbow-diagram-ROYGBIV.PNG