I always assumed its daily reporting of monthly active users. the nodeinfo format that is used for reporting the data does not show daily active users iirc (it is seemingly capable of reporting weekly users).

FYI, its not true the 80 percent of users are on lemmy.world see here (total number of active users) and here (number of lemmy.world active users).

Also piefed as far as i know does not really support multireddits , you can’t define a feed of groups of communities as a user. piefed topics are configured by admins or the developers .