The Enchantment "Critical Hits" does not add it's 3x damage multiplier when damage is dealt by weapons that create explosions on contact, example being the Exploding and Implosion Crossbows you can get from the Fiery Forge.

Upon either weapons projectile making contact with any mob, the explosion(s) will always deal their base damage, meaning the critical hit modifier of 3x does not get applied at all, effectively wasting the player's enchantment points on something they thought would be nice to have.