Regurgitation is when food is expelled from the esophagus and it usually occurs within 24 hours of the meal. Regurge generally doesn't smell very bad at all. Vomit is the prey item, partially digested, being expelled from the stomach. This can happen days after a meal. The smell is unmistakable and horrible. There are many reasons why a snake could regurge or vomit up a prey item. They include but aren't limited to:

Internal parasites
Improper temps for digestion
Stress before during or after feeding
Overly large prey item
Obstruction
Dehydration

If parasites can be ruled out, the most likely cause is a husbandry issue. Check your temps, humidity and make sure there are adequate hides available. Hope this helps!