I kinda disagree with him on this point. I wouldn’t necessarily limit to one thing, but I think functions should preferably be minimal.
I do actually agree with him on that point - functions should do one thing. Though I generally disagree on what one thing is. It is a useless vague term and he tends to lean on the smallest possible thing a thing can be. I tend to lean on larger ideas - a function should do one thing, even if that one thing needs 100s of lines to do. Where the line of what one thing is, is a very hard hard idea to define though.
IMO a better metric is that code that changes together should live together. No jumping around lots of functions or files when you need to change something. And split things out when the idea of what they do can be isolated and abstracted away without taking away from the meaning of what the original function was doing. Rather than trying to split everything up in to 1-3 line functions - that is terrible advice.