You need to analyse the role of the flashback which we are told about just before the end of the story. In this flashback, we are persented with the two men as children, and how they together caught a crane, and then realised that its freedom was worth more than anything. Consider how this release of the crane is described:
But the next moment, as another crane from a nearby bush fluttered its wings, the boys' crane stretched its long neck with a whoop and disappeared into the sky. For a long time the two boys could not take their eyes away from the blue sky into which their crane had soared.
Clearly the way in which the boys are mesmerised by the blue sky shows the way that they value freedom more than capture. The decision of Songsam to therefore let his friend escape and enjoy the same freedom indicates their understanding that freedom is infinitely more important than capture, and also symbolises how the strength of friendship can overcome the power of competing ideologies.