It's a reward for taking steps in his development.
Why is it that everyone always infers that it definitely means something about someone else?
Holzer was just up. He struggled to hold down his end of his pairing's bargain. It was clear he was lacking in confidence, and needed time with the Marlies to continue to work on his game. He was also easy to put down, not be subject to waivers. Liles gets games in, and plays pretty well, shows mobility, and strengthens the team's ability to move the puck. He then gets hurt, and we need an extra D-man for insurance.
You don't yo-yo Holzer. He's there working on his game. The best thing to do is exactly what Nonis did. Take a kid who has taken strides in developing his game, and reward him with a call-up. Give him a taste of life in the league. The travel, the routine, the atmosphere, and the paycheque. It's a carrot. He may get a game in, to see how he steps up to the pressure of playing with the big club, and we can all hope for the best that night. But this is going to wake up the hunger in him to really push for next year's camp. This is the kind of motivation that developing players live for.