It matters specifically in the case of making legal arguments.
I'm not saying the board was right, but please see it from their perspective. A certified traffic engineer would also use the term "engineer" in his findings. The latter's analysis would be given much more weight, be trusted more, simply because that's what certification is meant for. We've created titles and institutions for a purpose, so that Average Joe Board Member doesn't need to go into the details of a technical analysis, but can trust the outcome proposed/suggested.
Sure, if we're talking about some kind of complicated physics and structural calculations, with lots of technical jargon - yes, involve the engineers.
But we're talking about some simple math for counting the length of traffic lights. Everybody uses traffic lights, everybody knows simple math. It is ridiculous to assert that you need a technical qualification to know it's wrong that red light cameras flash at 100 seconds, but the light changes at 110 seconds.
I don't think anyone is disputing the law beyond claiming that it's stupid.
And, in this case, the board members were all certified traffic engineers and were reviewing this other person's offered analysis (or, rather, deciding to go after the person for their affront in even offering the analysis at all without having a certification). As others have pointed out, Oregon is very selectively enforcing the law. It's pretty hard not to conclude that some asshole decided to go after someone for pointing out problems with work for which they were somewhat responsible.
I don't need to be a chef to know when the meat is spoiled.