I would be looking at the "Dielectric strength" on that table, which is given as 20MV/m, meaning a breakdown voltage of 32kV for a 1.6mm board.
I think the table is kinda unclear, but I believe the (A) in parentheses is indicating a 1/8" thickness (based on rows 8 & 9), which works out to 63kV breakdown voltage, which is indeed greater than 50kV.