If the argument is "he said he was an 'engineer' and he isn't licensed", that's fine. And the Board's Final Report contains a lot of language establishing that, and for that he can be fined.
But the Board's Report goes out of its way to say that ORS 672.005(c) and ORS 672.002 define "practicing engineering" as quite close to just "calculating the hypotenuse of a triangle in public", and that just practicing engineering in this manner without registration is not allowed. Check Section 14 of the Final Report. It makes no reference to "purporting to be an engineer": it's "by [critiquing an engineering formula] and submitting the critique [...] to members of the public" [...he...] thereby engaged in the practice of engineering [...] specifically, traffic engineering [...and thus] violated ORS 672.020(1), 672.045(1) and OAR 820-010-0730(3)(c)".