That man died only because of Fiona.
There wouldn't have even been a battle without her.
Or are you going to deny that?
I am, because that's not what happened.
It's true, that Fiona disregarded the purpose of the legal gathering and put another agenda on the table, which she had the legal right to do as the Grand Enchanter, and that stirred up some templars. But Lambert interrupted the meeting, not because of that, but because he said he was declaring the gathering no longer valid because Pharamond had been murdered and he was taking Rhys into custody. Fiona responded that they had the legal right given by the Divine to be there, and Lambert responded saying that Divine's authority no longer mattered, then ordered the attack.
Yes, Fiona didn't help matters, yes some templars were provoked, but in any court of law, in any country I can think of, the person who throws the first punch is always the one who starts the fight. Words, and being provoked, never are justifiable reasons to throw the first punch in the courtroom, and is usually thrown out.
Lambert and the templars launched the attack and struck the first blow, regardless of what Fiona or the mages said, and that means they started the battle.