Because this may not be a "free speech" issue at all.
Go back to my previous example. Is it a matter of "free speech" if I call myself an attorney and I have no professional training as an attorney at all?
One may always act as one’s own attorney. Sacrosanct.
The exception that should apply here as a citizen using the roads is his own personal interest. The right to petition for redress is sacrosanct. His engineering may actually be better than the so called Engineers’ and the constitution gives him the right to argue it to his own interest.
“1) In order to safeguard life, health and property, no person shall practice or offer to practice engineering in this state unless the person is registered and has a valid certificate to practice engineering issued under ORS 672.002 (Definitions for ORS 672.002 to 672.325) to 672.325 (Civil penalties).”
https://www.oregonlaws.org/ors/672.020
He didn’t practice any professional engineering in this case. It’s overreach.
That depends on whether you take a case as an attorney. This man performed his own study, paid by no one, and truthfully identified himself as an engineer (in accordance to his degree).
If he claimed the title of Professional Engineer, perhaps he is wrong here. But the article says he called himself an "engineer", not a PE.