It's not bizarre at all. You have multiple drives dropping out of the pool randomly all the time without the ability to reconsile with a zpool scrub and you *will* get corruption. There's nothing shocking at all. In fact, when I saw his first output I figured the pool would be done for, the question was whether it would even mount or not. :p
I also thought it would be wiped out. But seriously, I do think it is bizarre. Look at the math: He had to get 6 out of 12 drives to, in that (proximate) instant, write corrupt data for that particular metadata block. Remember, metadata is written twice, and with two vdevs, one copy goes to each vdev. His metadata corruption is absolutely astonishing, and to still have a semi-functional system? Amazing.
That's why I tend toward running the memory test on ECC RAM. It's more believable!