I don't understand, why doesn't he just sell it on Yobit since it trades on there ?

When is opening day? And what was the ICO price ?

It's IOU on Yobit, I cannot transfer Lisk to exchanges yet.

But how will you transfer the lisk? Are you selling the associated email too?

Trusted escrow for now....
When Lisk launches, The Lisk will be transfered to buyers' account.