I can see why they think that. For really advanced stuff MATLAB is faster. I personally would prefer using a combination of Mathematica and C++, but it depends entirely on what kind of math you're doing and what you're used to.
Mathematica is pretty great for its user friendliness and intuitive coding, but it's also less fast for really complicated stuff -- not that you'll come across those sorta things in your undergraduate degree more than once or twice I think.
In Mathematica it looks much better in my opinion. Plus, you can customize a lot of things in the display, though not as much as I'd personally like. For example changing the fonts in display can only be done to a limited amount, and plot legends and axis labels have very few customization options in terms of style. But one thing that is great is that I can combine arbitrary graphics objects really easy (e.g. combining parametric plots with vector fields, adding random circles or points, combining plots with list plots (data plots))