He is wrong. Proprietary software is near impossible to escape. Try running exclusively open source is impossible (sadly, for those of us who like to keep prying eyes out of our hardware). It's in the firmware blobs we load, embedded in ROM's in things like SSD, in the digital thermometer on my desk, the monitor my computer is connected to, the IP phone I use, in the modems in my mobile, in the batter control chip in my laptop.
But to a programmer, I guess it may look like open source is replacing everything else. That's because we programmers have gradually have replaced everything we use with open source - compilers, editors, web servers, libraries for just about everything. Even stuff we use play with rather than get paid for is replaced - like photo and video editors, 3D printers, model plane piloting software.
It's easy for us, and cheaper in the long run, and given enough time the end result is better quality than the proprietary stuff because we all pitch in to knock off the paper cuts.
But it really is a case of "scratching itches", so if a programmer doesn't get itchy about something then it usually won't have an open source version. It's not hard to find examples. There are some usable PCB design tools out there - but 3D mechanic drafting tools weren't a thing until 3D printers tickled our interest in that area. Anything that requires specialised hardware is going to be out of reach - so you won't see open source MRI scanners, but I have no doubt you will see devices using 2 cheap web cams to do SLAM in the not too distant future.
This has had the accidental effect of making us more efficient. Any tool we can conceive of that allows us to do our job done better is free. The tools we already constantly get better - for free. In any other industry this might be a problem as supply overwhelms demand, but we seem to be in the odd position of the world demanding what appears to be a near infinite amount of software.
I am constantly amazed by how the demand for good programmers never seems to tail off. Even where I live (Australia) which has very high wages by international standards, and in the face of huge numbers of programmers coming out of low wage areas, _and_ in the face of jobs being some of the most transportable on earth, anyone competent programmer who wants a job gets one within weeks. I think we partially have open source to thank for that.
But step outside of what programmers want, and we are as mercenary as the rest of them. We are more than happy to develop nice new shinies we use and give them away for free, but we know who butters our bread. We don't write code for them for free. And since we are all getting paid, that must mean most of the code we write isn't available for free.