But my understanding was that at 6 blocks/hr difficulty shouldn't increase, even if its only ~4%
Yes but about 400 blocks were completed already. It may be 6.01 blocks per hour right now (in fact at this second it's actually 6.36), but for other times during that 400 blocks it was higher than 6.01, so in total, an average of 4% more than 6 blocks per hour was completed. The average speed will continue to change over the next 1600 blocks as the hashing speed fluctuates.
Thank you! lol I knew I was missing something, didn't account for past recent higher generating speed.
/thread =)