Hard to say because Malaysia esp Semenanjung, historically does combined federal + state elections together, so that does lead to historically high turnout (and compared with worldwide we're historically on the higher end of voter turnout). Theoretically and based on other countries, non-federal/general elections don't elicit the same rates for various reasons. What's interesting is that we're still pretty high (compared to general worldwide trends) but, depending on how you see it within Malaysia, certain states "feels" lower (in quotes because there's really no comparator. Thevesh on Twitter went with GE15 numbers based on the fact that voter behaviour is likely the most similar (these elections after all are "delayed" in popular understanding).)

What the lower turnout (in some states! All are lower than GE15 but depending on state, is of similar trend of high turnout, adjusted for the perception of lower stakes a non-general election usually is treated) means is still too early to say. Usually it indicates an emergent consensus that the election offered no good choices.