This is something I ask myself constantly. I believe what the commenter means is that if you want to "grow" or get a higher salary then you will be expected to do more, and at a certain point the definition of more can only mean stepping into a leadership role of some sort where you have to interface with more people.

If you're happy with your current responsibilities as an IC then you should be able to stay at that top level (Principal engineer) and continue doing what you're doing today, just don't expect a higher pay.