why did the protagonist choose to go a different route to get to the camp where his buddies were going to meet him?

The answer to this question can be found in the first paragraph of the text. The man chose a different trail in order to save time.

"Day had broken cold and grey, exceedingly cold and grey, when the man turned aside from the main Yukon trail and climbed the high earth-bank, where a dim and little traveled trail led

eastward through the fat spruce timberland. It was a steep bank, and he paused for breath at the top, excusing the act to himself by looking at his watch. It was nine o'clock."