Programming languages exist today because computers can't handle ambiguity and don't understand software design. In another 50 years, machines will be a lot smarter, more able to handle ambiguity, and better than people at designing workflows and catching potential errors. Like the horse, no doubt some people will still prefer to do things the old way, but there's a good chance this will be limited mostly to academic exercises.
All they're saying here is that the tools we have will progress a lot in the next 50 years. There are some obvious problems with the way we design software right now which are due to human limitations. The only way to fix those is to remove a lot of direct control from humans and give it to AI programmers. Manually writing JavaScript in 2066 will be like manually carving arrowheads today: still effective but not something you would do for a serious purpose.