My crank fell off, how do I re-attach it?
In general, crank fixing bolts need A LOT of torque.  This chart list torques for several varieties of crank arms.  (I suspect you have a variety of Octalink.)  You're probably looking at something in the neighborhood of 350 inch pounds, which would be 35 pounds applied to a 10-inch lever arm.

Too much force and you shear the bolt.  Too little force and the arm works loose again.

The torque spec embossed on the bottom bracket cup is most certainly for the cup, not the crank arm.

Unfortunately, if your crank arm fell off I suspect it's been damaged, and is apt to no longer fit tightly, no matter how tight the bolt.