What you are saying is that he should not learn C++.
For further questions, refer to the C++ Frequently Questioned Answers.
And the subset argument, although it has some truth in it, is misused a lot. Sure, I do not use all of the C++ features, but how can you choose a subset well if you do not have at least an idea of most features? And the well-chosen subset can be different from project to project. I see C++ in a similar way to a large toolset (I mean a metal/plastic/wood toolset, not a software toolset). You don't need to master all the tools in a toolset to do a particular job, but you should have an idea of most of them.