I don't know, and to be honest I hadn't noticed.
If I had to guess I'd say the picture was taken and published before all the legal avenues had been finished, meaning he was still at the stage of being innocent until proven guilty. It's still obvious that he's handcuffed, but then again bodies of suicide victims hung by rope and genitalia are obvious even when pixilated, but they still do it.
Of course this doesn't seem to happen to everyone who's arrested and cuffed but he might be important, and or wealthy enough to not have the cuffs shown.
Plus of course, "this is Thailand".