I think you're both right, but you might be thinking of different tasks and libraries. If we're talking about solving a specific type of PDE, then in that scenario he's probably right that MATLAB will work better out of the box, but if we're talking about logistic regression on data from a messy CSV table, then python will work great and have better usability than MATLAB (IMO). He might also be thinking of versioning and packaging headaches in python, which are quite a pain the first time exposed to them coming from a walled garden environment.