Let's look a little closer at it.
8:58 - Shield Samba goes up
8:59 - Divine Veil goes up and Curing Waltz gets fired off early wasting the heal from both
9:00 - AoEs start hitting
9:01 - Shake it off goes up
9:05 - Tank LB3 goes off soaking the last two hits
9:06 - Mechanic done, no one died.
A few observations from that. The reaper and dancer came closest to dieing, everyone else was pretty safe.
If they had have had the full 8 people for the stack, it wouldn't have been nearly as close and secondly, they could have made it safer for themselves by not wasting Curing Waltz or the heal portion of Divine Seal early (That's 10k hp or roughly 20% of a HP bar wasted right there). I also suspect that no one used Feint looking at the scrolling text. That's another big chunk of mitigation gone.