I don't have the full story because it happened in another business unit, but one of the worst outages I ever worked the rumour was it was caused by someone doing prep work for a later cutover to new hardware. Whatever they were doing to prep for the upcoming cutover, the router rebooted. They didn't know it rebooted, so they did the same thing to the secondary and tertiary a few minutes later. Also happened to be on a Friday.

So sometimes it's easy to rehearse all the critical stuff, and get a bit complacent with the stuff that is just expected to work, plugging something in that's not configured and getting it ready for the big migration. And it's hard to get a 100% perfect replica in a lab. So I think odds are you're right, but I think there is also a longer tail of possibilities as well. And in my experience, there is always tension between chasing the 9's of availability, and getting some "safe" work done when convenient.