kind of a no win situation here
The 10% for a win is reserved for a player's regular tour caddie. There's even usually a contract for this. If your player is a top 20 tour pro, a caddie can make quite a good living. The caddies who get these full time contractual tour caddie jobs are either very good at it, or they are a friend/family member to keep this generous pay in house.
The only way a pro takes a local caddie is if the regular guy was just fired, or can't make it for some reason. Or if the pro doesn't play often and gets in on a last minute exemption etc. This total each week might be 5-10 players out of a field of 150.
The local caddie either just waits til the end of the week and sees what they make, or they agree a pay plan up front with the player. In this case they agreed up front $4000 if Kuchar made top 10.
Kuchar ended up winning, which is quite rare with a sub caddie, and paid the guy $5000 - the agreed $4000 plus a bonus for winning.
so in theory nothing wrong with the deal.
Problem is the regular contracted tour caddie would have made $130,000 for the week. Someone got in the ear of the local caddie that he was really stiffed, so he complained. With the 130 v. 5 difference Kuchar now looks cheap no matter what he does.