The main difference between biltong and beef jerky is the drying process. Beef jerky is dried in a dehydrator or oven at around 160 F for a few hours up to a few days. This fast intense drying process gives the beef jerky its rough and stiff texture. On the other hand biltong is dried naturally in a cool dry space for 12-18 days, depending on the environment. The slow drying process allows for the nutrients and spices to soak into the meat and results in a wonderfully tender texture.
The next biggest difference are the spices and ingredients used to prepare the two foods. Beef jerky often uses liquid smoke and spices more on the sweet side (the popular store brands put many unhealthy ingredients to keep the jerky shelf stable for years). Due to biltong being traced back thousands of years, its main spices are simple and healthy. The core ingredients are salt, pepper, vinegar*, and coriander seed. Other spices may be added to compliment the core flavors.
*The very low PH of vinegar (2.4) kills the bacteria