He agreed to a deal with a seller and once escrow was setup he backed out of the deal. This is a sign that he was trying to avoid using escrow and only agreed to accept escrow to avoid setting off any red flags to others. Despite this being a bad idea, often times people will simply agree to trade without escrow if one does not respond and setup escrow quickly enough.
A neutral rating is more appropriate then, since no coins were lost and no scam was attempted. People are allowed to back out of deals. You should put in the rating your belief it's a sign he was trying to avoid escrow.
The scam that was attempted was that he tried to scam the bitcointalk account from the seller. The reason given in this thread was something along the lines that he did not trust me, however that is contradictory to the fact that he asked me to escrow for him.
The note in my rating does give facts that would make a reasonable person believe he was trying to avoid escrow.
IMO once escrow is setup for a deal it should be pretty much set in stone. As if you are selling something the seller may send what is being sold right away assuming that the escrow is going to be funded (this has happened a number of times if you look at various escrowers' sent negative ratings). The only real reason to back out of a deal once escrow is setup is because of some significant change in circumstances, for example didn't receive money you were expecting, and canceling a deal should be mutually agreed to, meaning both parties agree.