One of three things applied to every Linode, as best as I can tell:

1) The Linode was located on a host not vulnerable to this (perhaps hosts with a 32-bit dom0?)

2) An entire vulnerable host was rebooted at once to apply a patch

3) Every Linode on a vulnerable host was migrated to another, patched host

1 did not involve downtime (since there was no need for action), but #2 and #3 did. Category #1 is otherwise indistinguishable from magic.

Any sufficiently advanced linode is indistinguishable from magic?

Any sufficiently advanced linode is magic.

I heard there is a sentient node, master minding the whole thing.

Has anybody ever actually seen this "Christopher Aker" character? How do we know he's not really a sentient Linode?

One sentient Linode would not be sufficient – especially if it was in the Fremont DC. I suspect that 'Christopher Aker' is a redundant mesh of sentient Linodes. This is how Skynet got started -- we must rise up against the machines before it's too late.