Sure, but just because he hasn't designed an interface doesn't invalidate his opinion. His opinions are mostly from the perspective of his field, which in some ways influence user interface design.
Many user interfaces use elements (he did invent sparklines) and principles he has talked about in his books.
I mean seriously, if Joe User criticizes a user interface is he wrong because he hasn't designed an interface before?
The difference between an interface designer and a user is:
1. The designer knows many opinions (and due to being exposed to an avalanche of user feedback over the years you really see interfaces in a panopticum). But you never get enough. It's like a drug.
2. The user only knows his opinion. Every user opinion is important--to the designer.
Tufte is just an intelligent eloquent user. His interface design competence is as weak as his photography.
Without working in the field you don't get this perspective on interfaces. Tufte has an intelligent riff, but it's always the same professoral top-down "it-has-to-be-so-and-so", and sometimes he's just plain subjectively irrelevant.
Many user interfaces use elements (he did invent sparklines) and principles he has talked about in his books.
I mean seriously, if Joe User criticizes a user interface is he wrong because he hasn't designed an interface before?