LongBeach – not necessarily is the person “believed” (that he actually owed the other person money) but possibly because he is obligating himself to pay that person the money. (The difference would be if by “admitting” the debt, he causes damage to another). By issur, a person makes the object ossur FOR HIM, but not factually ossur. Likewise by monetary matters, it may not be factually a debt but it becomes one on him now.
I never understood the expression “like a hundred eidim” – since the testimony of two eideim is equally as strong 100 eidim, why use the (misleading) term “like 100 eidim” which implies greater validity to 100 eidim over a smaller number of eidim???