IDK, I do agree that he's immature in some ways. I don't like all the podcasting and talking about other teams when your house isn't in order....
But what did he actually say about McCarthy? He said he's not worried about his future and that Martin has given more to the Cowboys, which is 100% true. McCarthy has given them sweat for 5 years. Martin has given them blood, sweat, and tears for 11 years. Martin's about to be done as a player. McCarthy can get another job coaching if he wants to (although with NFL HC probably out of the question).
He was asked about McCarthy and said he was sadder for players. I take it as maybe a little bit of a dig, but I think it's mostly just a players love players thing.