Maintenance for the week of November 4:
• [COMPLETE] ESO Store and Account System for maintenance – November 6, 9:00AM EST (14:00 UTC) - 6:00PM EST (23:00 UTC)
Is this just the tooltip you see while preparing to queue that shows the 300k? My suspicion is that the event is applying an IC xp bonus when it's showing you that tip, but that if you were to actually queue and run a random dungeon, that you'd only get 100k because you weren't in IC when the xp is awarded. I'm guessing somewhat though.