Again, the very definition of overperforming in the dictionary is to perform better than expected, so the numbers on their own mean nothing.
A few years back, after the original Aquaman, the second entry would have severely underperformed, but after constant box office disasters, especially in the DCEU where the film did almost what the rest of their slate managed to make last year combined, the film overperformed for sure.
You can have an extremely successful movie underperforming and a box office bomb overperforming, if box office doesn't align with studio expectations. It's as simple as that.