Hearthpwn

Couldn't see any reason for it.  Note in the mouseover in the screenshot, he shows as 7/6 with no additional effects, but on the battlefield he's 6/2.

I had an alarm-o-bot come out as a 6-2 thanks to swift messenger.. 

So that's why my opponent played 5/2 Bonemare.

This is definitely a bug with worgen Rush minions that swap stats at the end of the turn, cards like Shifter Zerus and Chameleos bug out when they transform into them and the stats get swapped at the end of turn. The stats then remain for any new card they change into. This bug has been around pretty much since the launch of WW, apparently not important enough to get fixed yet ...