Second pic shows the lower radiator outlet which is a couple inches above the drain plug. Doesn't seem to me that should be wet if the issue were the plug. Also if the o-ring on the plug seal were failing it should just be pouring out the little spigot below it.. that's the whole point of the spigot.
Take a picture of the top tank of the radiator, especially the area around the small flat area with part number writing on top of it. I'd be surprised if your mechanic left a failing radiator in amid a valley plate reseal but stranger things have happened.
