That really has nothing to do with the first three bosses who have already been killed.
You have a point, Mihir, about learning encounters. However, I should also mention that you had more ilevel on your first Spirit Kings kill than I currently have right now. By the time you started doing Meng first (a month later?) I'm sure the gear gap got even further. It's a bit different when you have the tools for the job.
Gear doesn't make you dodge fire faster.
I would imagine the data comes from the same place your achievements and statistics come from. Blizzard records your wipes on bosses ( which is why in statistics you can see what boss you've wiped the most on), it just doesn't show up in your statistics page.
Pretty coo, feature. I've noticed some weird discrepancies, but most were fixable by updating. People need to log off like they do for guild achievements.