The Curse of the Bahia Emerald
wired.com
wired.com
Note that it looks to be more than half matrix, with the remainder being actual gemstone.
Also, like many other gems, the price of a gem varies wildly with its clarity, etc.
So the worst case scenario,I suppose, is that it could be that the stone is only worth its weight as rock dust. But generally I agree with you that it seems unlikely, and it's probably just hyperbole.
"On the packing slip he wrote “rocha: rochedo—rock” and listed the value at $100."