Too emotion because he put his sole and heart in it, which shows he truly loves Yuna. When a loving couple breaks up, one side may tell his (her) friends that how unfair the other party was. It does not mean it is out of vengence. It is simply "too emotional" as you said, and it is unwise and may become hurtful to both.
In Brian's every interview, he critized only how he was treated and never attacked the other party in a personal level and even suggested a room for reconciliation (e.g., he said he will still coach Yuna if she and her mom decide to). However, I got the impression that Yuna's party was full of personal attack (e.g., calling him liar, and now the statement in response to his revealing the LP music saying, "This can only be construed as a move intended to hurt the skater'').
They both are hurting each other, one side unintentionally, the other on purpose and maliciously.
It is my impression that Yuna camp kept their mouth shut not because they didn't want to disclose the reasons, but because they had no good reasons. They have been waited and waited till Brian made a mouth slip and finally found a good reason to fight back.