Tried it myself, and it seems to be a problem with the encoding of that particular video, or WiiMC is using a codec that’s not fully compatible. Audio on that DB chapter was off-sync on my Wii too, but I immediately tried some Ranma 1/2, Azumanga Daioh and Slayers MKVs, and they all worked fine (both audio and subs) with the same settings.
On my PC I still noticed a 0.2 second offset between audio and video, as Goku started moving his mouth just a bit before the voice started… and on WiiMC with the default settings, the delay is about 0.8 seconds.
You can adjust WiiMC’s audio delay by going to settings/video, and if you add a 0.6 or 0.8 second delay, it should fix it for this particular case.
From time to time I too have gotten some MKVs that don’t work properly, even on PC. MKV is a container format with support for a lot of different audio and video codecs, and sometimes people use some obscure or outdated codecs, some newer ones that you don’t have installed and cannot play properly, or they just do a terrible encoding job.