Assuming two medium humanoid types with 5ft reach are the grappler/grappled and the thorn whip pulls the grappler 10ft against their will towards the caster. Does this satisfy the conditions to end a grapple per the final point of the grappled condition, quoted below:
The condition also ends if an effect removes the grappled creature from the reach of the grappler or grappling effect, such as when a creature is hurled away by the thunderwave spell.