I'd be interested in seeing the source for that. It would seem to be a chronological impossibility, as the earliest Tocharian A documents date from the 6th century CE, which is centuries after even Cai Lun paper.(SRC)
BTW, the oldest paper ever found was found with this area and it has Tocharian A written on it.
It's contained in the book,The Tarim Mummies, linked in post #10.