I'm not familiar with their shipping arrangements, but remember the item is coming from china..they may have shipping arrangements with their carrier for 'up to a set amount of weight, for a set price'..Some companies do this as it helps the buyer save money when buying in quanity..In other words they can ship 10 units for the same price as shipping 1 unit...
Just contact them, they are normally on here quite a bit and seem to always answer questions very quickly...They seem to be building a good reputation with the members on here..