the 'A bonus of [495k] and 9,900 gil' message is a system announcement message stating the total experience and gil you obtained from the roulette bonus. Not added onto the experience message above it.

Its basically saying:
[x] exp has been acquired
"Hey! you gained a grand total of [x] exp and [y] gil as a bonus from queueing in a roulette"

Redundant and dumb, i know. But not a bug.