This is an bug which was already in before trials and it still is in the game. Sandstorm Warrior can be triggered by other defenses of the Mystic too like Serpents Coil or Sand Vipers. The description of the Shard says "The Snaking Sands sandstorm ...", so it should not work for Serpents Coil or Sand Vipers.
This allows the player to increase the Hero damage and Ability Power way more easily then with Sandstorm for all these defenses need to do is target an enemy to apply the buff. By placing multiple Serpents Coils and Sand Vipers down you can easily apply the buff multiple times. Also the Buff stays for the full duration even after the enemy dies, with that the towers target another enemy and applying another layer of this buff. If you use split vipers on Sand Vipers the tower will apply 3x the buff in one go.
It is clearly visible that this shard should not work on Coils or Sand Vipers for it is way to easy to use this powerfull damage boost with them.
Steps to reproduce:
The Sandstorm Warrior Shard only works on Snaking Sands.