What evidence does the old swamper give that the ranch boss is a “pretty nice fellow”?

The boss gives the men a gallon of whiskey to share during the Christmas holiday.

"Well, he’s a pretty nice fella. Gets pretty mad sometimes, but he’s pretty nice. Tell ya what—know what he done Christmas? Brang a gallon of whisky right in here and says, ‘Drink hearty, boys. Christmas comes but once a year.’