To my knowledge the instruction from Sedo (after they receive payment in their account) Is to both unlock the domain AND forward the transfer code. Reads to me that they have notified you of a Potential sale, They have to tell you of the new status as the homepage changes to "Pending Sale" This is probably an Invoice requested (by the buyer) sale. Unlocking the domain alone is not going to affect anything.
Sedo are not going to pass onto you any specifics regarding refused payment-method, non-matching address details etc. Unfortunately it just becomes an uncompleted sale. I'm sure we have all had them at one time or another.
If your into the risk-game then just relist it (with resolving homepage) on another platform. More likely the buyer wont return though.
It is sometimes too easy to see a Sedo sale notification email as a done-and-dusted transaction, when that is far from the case, Can't remember the amount of times I've been left on tenterhooks waiting for the transfer instructions. Did have a domain go through them at $1400 this week. (basic 10% commission) So I rarely complain about their service