Owlbears do indeed lay eggs. One of my personal favourite features of AD&D 2nd Edition is that most every monster entry includes details on their appearance, behaviour, social organization (if any), habitat, and ecology. The ecology notes for the Owlbear in the Monstrous Manual read in part:
[Owlbears] are warm-blooded mammals, but lay eggs. […] Owlbear eggs are worth 2,000 silver pieces and hatchlings are worth 5,000 silver pieces on the open market. […] while they are impossible to domesticate, they make formidable guardians […]
The full entry is a small essay packed with details like this.
The richness of the 2e library regarding canonical monster lore is nearly unbeaten to this day, the only possible competition being the 3.x hardcovers focused on specific monster types, such as Draconomicon and Lords of Madness. An AD&D 2e Monstrous Compendium or Monstrous Manual is well worth owning for lore aficionados regardless of the actual edition being played.