Yeah, that peak is from the free play period they held. The days before the Humble Bundle reveal saw peaks of around 30 or so, with long stretches where it couldn’t even reach 10 players.
Honestly, it feels more like a desperate bid to prop up Rapture Rejects itself. Revealing it early gets new owners to install and play it, which props up the player counts, which makes the game look healthier than it is. If Humble had waited, it might have been completely dead by the end of the month. And that would have looked even worse for Humble.
My guess is that when Humble signed the deal to feature Rapture Rejects, it wasn’t yet known just how much of a bomb the title was going to be. It had a license (Cyanide and Happiness), it was relatively heavily promoted, people who played it before release seemed happy with it. And then it all fell apart.
EDIT: This is really looking like a dud bundle. The Division’s sequel releases March 15, which will most likely cause The Division’s player base to evaporate. Worse, Humble only gave the cheap base game. Now Rapture Rejects is truly wasting a “new game” spot in the line up, and I mean that in the actual sense of wasting a slot on a dead game, not in the “I just don’t like this so I’ll say it is a wasted spot” sense.