The thing was, the Dragonlance Adventures setting book was published after the original adventures and novels. And it made much bolder changes to the D&D core rules. It basically replaced magic users, illusionists, clerics and paladins with new core classes, wrote out druids, and introduced minotaurs as a replacement for half orcs.
So, from the start of Dragonlance in 1984 to the publication of Dragonlance Adventures in 1987 druids were part of the setting, appearing as NPCs, and potentially as player characters*.
*Because druids and paladins required high stat rolls in 1st edition, they were expected to be rare.