Its kind of a bug; although the API for search can take in all those sort types, it actually can only use a few of them, so TopWeek gets turned into TopAll. This is because when searching for All types, many of them have no concept of TopWeek, like a search for users.

In lemmy 1.0 I'd like to fix this by showing a specific set of filters and sorts for the given searchable item type: https://github.com/LemmyNet/lemmy-ui/issues/3995