I'm not excited about the pairings, but I could see the logic behind it is that we have a very tight schedule this month with 15 games in 29 days, he may be trying to spread out the ice-time and have multiple effective but not elite pairings.
The other one is, we may be trying to see if we can get Zaitsev to a level of a competent top 4 player who can live up to his contract. Trying him with Muzzin who is an effective defensive defender and strong possession game, we get to see what he is with a more consistent partner compared to the more dynamic Rielly and Gardiner.