As someone who (as ps player) used to raid savage with someone whose addon-bot-mod-whatever calls we all could hear blasting through his headset second before anything we could react to appeared... I don't know, my dudes, I'm occam's razor kind of gal, and though both explanations are simple:
1) the tank in op's story had some very good luck and dodged everything flawlessly 5 seconds earlier than any reaction demanding signs appeared
2) the tank in op's story had a little help, with tool which is very common and easily available - despite being in gray area
-- I know which seems more plausible to me, but I think I'm gonna keep that to myself.