Agreed, he's making the assumption all design is related to digital. I do more development than design these days but am from a graphics background. I have worked with a lot of young and older designers who can't code but are hugely talented in other areas like branding, illustration, film, motion, strategy ect which I know nothing about. It's a big industry and there is huge variation in skill sets which is what makes it great. His second tweet gets more snarky - https://twitter.com/Allan/status/535161991149932547