We’re talking about the meaning of “malfunction” here, we don’t need to overthink it and construct a rigorous proof or anything. The creator of the thing can decide what the thing they’re creating is supposed to do. You can say
hey, it did X, was that supposed to happen?
no, it was not supposed to do that, that’s a malfunction.
We don’t need to go to
Actually you never sufficiently defined its function to cover all cases in an objective manner, so ACTUALLY it’s not a malfunction!
Whatever, it still wasn’t supposed to do that