How did these grassy hillsides in Colombia become terraced?
These are terracettes https://en.wikipedia.org/wiki/Terracette#targetText=In%20geomorphology%2C%20a%20terracette%20is,them%20to%20move%20slowly%20downhill
  These are caused by natural earth movements as the slope angle is beyond the natural resting angle of the soil. These slopes are a result of rapid erosion e.g. by rivers and glaciers.
Solifluction https://en.wikipedia.org/wiki/Solifluction is a similar process.