I'm also confused whose finger got cut off
In the page before we see the finger, chapter 27 page 5, Jingi says "Gambling addicts can't quit even if you cut their finger off" then we see Jingi throwing a pen which lands in front of Heonjae as a finger, so it was either just imagery. Like the author demonstrating what Jingi meant or Heonjae imagining a severed finger.
the finger was just a hallucination but was actually just a pen, which you can see in the next panel :) (I think they just added it to emphasize the point that gamblers can't quit even if they lose a finger? not sure though)
OHHH, THANKS GUYS<33
DID BRO JUST PULL A FINGER LIKE.. OUT OF HIS POCKET??? I MAY NOT HAVE BEEN PAYING ATTENTION BUT WHAT????