Telling your interlocutor she sounds angry is basically cruising for the response "Well NOW I am!"

And I'm not so sure it's confusing justified anger with a lost temper so much as it is conflating them: you know, argument is always cool, argument is emotionless, anybody who brings emotion into an argument is the automatic loser, oh you GURL now you will proceed to cry as a manipulative tool, that kind of nonsense.

Also, I mean, has this dude been on the internet? Anger is not exactly difficult to come by, you know? To remark on it makes it sound rare and weird, whereas to my eye it's the calm and mutually-accepting airing of views which is rare.