Predict real world data after modelling with scaled features
I would say it depends on your training set. If you had a sufficiently large (and representative) training set, then you could say that the mean and the variance of the training set are the estimates of the population mean, thus, use these values also for the standardization of the one single testing sample. If it is not the case, then the whole idea of prediction is not really good.
Generally, it is wrong to use different transformations for training and testing sets separately. You can read about it more here