RED Is Coming - Southperry Sneak Peek

They can change the XP rates on any server at any time. The test server could have 20x XP right now because they were testing advancement prior the screen shots.
The whole point of a test server is to test things, so you have to take anything you see in one with a grain of salt.

What he meant was: When we have 2x now (for example), it's shown in two separate EXP lines. One for base, one for bonus. If the test server were running on 20x using the same mechanism, it should have shown two exp lines: one for base, one for the 19x bonus.
Of course, they could for whatever reason have left the old mechanism in place in the test server. One never knows with Nexon.