And K4 sooted is good enough to prevent a steal is it?

No its not id admit that the call was donkish and I was prepared to fold the flop if he bet- but he didn't which led me to believe that the river was a total bluff.
I called his bet and he shwowed A5o. He then started calling me DONKFISH for calling his bet - Can anyone else see that this is a bluff??? I was pretty sure at the time it happened. Thanks for the replys.