Hi,
after understanding what the number aside the green/red arrow in the tooltip actually refers to (amount of risen/dropped places since the last update), I finally found out what it means when the number is the same as your rank when in conjunction with a red arrow:
It’s a new entry on the leaderboard that dropped from rank 0 to the current rank.
That’s not very intuitive, though.
Suggestion: The grey arrow is being displayed without a number while the tooltip states something along the lines of “new entry”.