Uh, which prophecy? - it's slightly vague but bear with me ...
Psalm 41:9 (NIV):
Even my close friend, whom I trusted, he who shared my bread, has lifted up his heel against me.
... and ...
Zechariah 11:12-13 (NIV):
12 I told them, "If you think it best, give me my pay; but if not, keep it." So they paid me thirty pieces of silver.
13 And the LORD said to me, "Throw it to the potter"-the handsome price at which they priced me! So I took the thirty pieces of silver and threw them into the house of the LORD to the potter.
There may be other verses, too.
Now to you it's tenuous/nonsense, to me it's tenuous/nonsense, but there are plenty of Christians who sincerely believe this crap.
They believe that one of the twelve would betray their master, not because nasty God forced him to but because this particular apostle chose to do so - exercising free will, tempted by the money.
Edited to add: thank you Xanthippe - that was the scripture that I had in mind.