Not if your going to do a career in it as he said.
Once again we have interpreted him differently. I took "career" more generally.
It is to an extent, when you considering everything is basically already implemented for you in C#, and more so in Python. I didn't recommend he code an MMO, instead of hello world, I recommended he stick to what he already has experience with.
That is not to say you cannot learn in those languages, you can, but you will be missing the finer details.
Everything already implemented? If you're referencing the standard/.NET libraries: true, many low-level tasks are abstracted to save you from "reinventing the wheel", so to speak. But if he wants to write a web scraper, should he really be initiating the socket connection and parsing HTTP to do so?
As to missing the finer details: If you're referring to pointers/memory management/low-level programming stuff in general, then yes, he will be missing it at first. I'm not objecting to his learning low-level languages down the road. I'm just suggesting they may not be ideal at first.