The card is only triggering when the opposing player has a creature out. Based on the change to Prism Array (triggers on landfall regardless of opponent having creature on the board), I’d say this is a bug.
This might be happening with the other “Retreat” cards as well. Haven’t had a chance to test them.
Retreat to Kazandu does not give life if you don’t have a creature out.
I posted this a while ago, before 1.5 hit, and then they changed the way Prism Array works to what it is now. One would think the “Retreat” cards would be the same, yet they are not. This has to be an oversight imo.
Retreat to Coralhelm (Landfall: Disable the first creature your opponent controls until the beginning of your next turn and Draw 1 card.) does draw a card even if the opponent has no creatures. So it seems the behavior is card-dependent.