If a Beastman shaman takes the shard of the herdstone magic item, do they have to represent this on the battlefield with a suitable terrain piece?

I ask as I recently played against a Beastman player who made his own herdstone shard terrain which he said was impassable and was large enough to hide all his three Shamen behind all game. I couldn't find this rule myself, can anyone clarify it?

This was a tournament game not a friendly so I assume I wasn't being cheated.