The client does not send a seed.
It makes sense that the game state is only known on the server during the game otherwise your client would know which tiles are save which would allow you to automatically win. They can however tinker with selecting fields for mines that you (as a human) are more likely to click as there is no client seed involved.
That is actually a valid remark, the user needs to contribute to the process after the server decided on a secret seed. It is nearly pointless to employ a provably fair method like the one done by satoshimines (just read it up on their site).