According to the LN, Gringham started out as the third son of a common farmer. Since the first son got the farm and the second son was back-up, third sons basically became vagabonds when becoming adults. He also had no formal education to speak of, and so he speaks in a formal way so he won't be looked down upon for being an unrefined country bumpkin when speaking to patrons hiring his team.
That being said, he makes good money now, and his cut of the share this time around couldn't be earned by his two brothers in a year, so he was happy about how he'd done so far.
We'll so how he fares through this precarious situation.