Addressed numerous times in this post already, but (in summary) those were BAT grants given to Brave users from Brave itself, for the purpose of allowing those users to earmark tokens for certain creators. During a couple days in December, 2018, our UI/UX received a few major changes in response to tremendous user feedback. As a result, Brave tipping system is many times better today.

More details: https://brave.com/rewards-update/