Can you explain this death please?

Rip clip: https://youtu.be/4AEsYMgudJg

Character stats: https://ibb.co/p6dZBMYf

How could the character get OS by this? Res capped in Act 3 normal. Didn't find any clue on PoeDb. Is that a number thing I don't get or a bug? I need your help to understand please, thanks in advance!

Ok so this is one thing i think MAY be bugged, as i experienced it once also. It straight up 1 shot me also. I found that as long as I stuck close to him, he just simply couldn't hit me with it and he became easy again

That would explain a lot for sure. I posted it on the bug report section of the forum. Who knows.

Ok so it was a bug and has been fixed: https://www.pathofexile.com/forum/view-thread/3746117

"Fixed a bug where Doryani, Royal Thaumaturge's corrupted flamethrower ability was dealing significantly more damage than intended."