Let's quibble!

The phrase "A as B" tends to imply that "A" came temporally and causally first, then "B" was generated from "A" somehow. "B" is some kind of view, summary or transform of "A".

So I read "diagram as code", as that we have a diagram, and we are going to interpret it as code. We start with a diagram, and get code. A lot of visual programming type projects are in fact, diagrams as code.

Similar to the traditional text as (isomorphic to the) code (it is transformed into).

But "code as diagram", is what we have here. We are viewing the code, which came first, as a diagram which summarizes it. In a lossy but useful way. The diagram cannot be executed, so there is no diagram (acting) as code.