I imagine this line of argument can be made for about one million different jobs a year.
My lawn guy wants $30 bucks this week? I offered him $8. After all, he could have not had a job and made nothing.
Fact is "pay" is based on what others with similar talents and skills make for the same work. Not what you would make if you had no work.
This caddy was not familiar with Kuchar’s game - club distances, preferred ball flight, when to be aggressive, etc. Therefore his skill level was not similar to that of regular caddies of a tour player. So they had to settle on a different value. What’s not known here is what was the agreed upon percentage of winnings. If it was 1% then the caddie was paid appropriately, and shouldn’t be complaining. But I don’t read where the caddie is saying Kuchar didn’t pay the agreed upon amount; just that he’s not happy about that amount.