I received a ticket for driving with expired license tabs.

It's not incorrect for the officer to check 'traffic' because technically, a tabs violation is part of Washington's motor vehicle code; however, this kind of infraction is a nonmoving violation, meaning that it should not by itself affect your insurance.

However, this type of ticket COULD (but won't necessarily) affect a deferred finding but this depends on the type of deferred finding you have and the court in which you took your deferred finding.