All sorts of people talk about all sorts of things.
When someone who is famous talks about all sorts of things, it's fashionable to diss and mock them for "speaking outside their authority", yet everyone else is free to ramble about whatever they like.
You're doing an inverse arugment by authority here; "whatever Dijkstra says about [not-programming] is wrong and should not be listened to, because of who the speaker is".
Yeah, but he seems to be predicting the decline and fall of western civilisation because of unspecific use of language by young people these days. As there is no single definition of western civilisation, this is ironic as well as dumb.
The man in the pub may have a good point. If you read Djikstra's other essays where he wanders off subject, you'll motice he rarely does. He sounds like an angry old man, lost in dreams of a better past that never was.
Because though they are an expert in their small field, but no more informed or unbiased than your friend at the pub, they end up sounding dumb.
In this and some of other writings, he would do well to think and gather data about social issues, or talk mostly about algorithms.