I agree, it was most likely a fecal. Sometimes some of it doesn't digest all the way and comes out like that. IF it were a regurge, you would definitely smell it as such. The only way I could see if you could get a regurge after 6 days is if you didn't have any warmth in there to help the digestion, but then, the snake would regurge long before the 6th day if that were the case. So, I wouldn't worry about it at all.
When in doubt, use your nose, a regurge never fails to stink, even a mostly digested one!