since we have no ground truth nor have we (to our knowledge) received any alien signals to date, I don't see how you can determine performance in terms of accuracy; so maybe they mean an increase in processing speed
Edit: From the article:
> To train the AI system, Ma inserted simulated signals into actual data, allowing the autoencoder to learn what to look for. Then the researchers fed the AI more than 150 terabytes of data from 480 observing hours at the Green Bank Telescope.