Welcome back! The best procedure for any ticket should be to return the ticket with the “contested” box checked, serve/file a discovery request with the prosecutor, and review the officer’s statement for possible defenses.
We don’t have enough information yet but if you or he can later upload the officer’s statement and other discovery with personal info and ticket number redacted, maybe forum members can comment.
Probably he should read RCW 46.61.290 or any other applicable statutes and return to the location to take pictures. Then after examining the officer’s statement he probably will have a much better idea what if any defenses he has.
After requesting a contested hearing he still will have options to ask the prosecutor (if present) to amend to a non-moving violation or take his deferral assuming he is eligible.

