It looks like this isn't anything new, just . . . something that was never well-publicized. It's been around since at least late 2012, and probably longer - so definitely not new.
I don't think you can search all of a site's hot network questions from this interface; you can do it per-tag by the link
and just substitute in the tag name for
tag-name - or click the "more" you see at the bottom of your image. The default seems to show the hot answers from the last month, sorted by score, in most cases, but you also select day, week, year, and all time. But you can't sort by date or activity.
That said, you can use Data Explorer to solve the problem and perform a query of your own; this became possible a couple of years ago when entering the HNQ started to be logged in a question's history and is therefore in the
PostHistory table. You could probably pretty easily modify Glorfindel's SQL query from that first link to take the returned list of hot network questions and show their answers instead, add fields to include or exclude certain tags, or sort by different answer features, like votes or recent activity.