One behavior is inherently childish. One is not. One is objectively the attitude of an infant and thus does not require the act of infantalization in order to be framed as such.

No, it isn’t, and this is a subjective opinion on your part. Not everyone agrees with you, so it’s not objective. Even what exactly is ‘childish’ behaviour is subjective, and arguably culturally dependent.

His behaviour is pretty much by definition, that of an adult. An adult with poor impulse control, poor anger management skills, sure. But childish? That’s a value judgement which contains no insight likely to reach anyone. It adds nothing to the conversation.

Use less reductionist words to explain why it’s bad.

Or to rephrase: Linus’ reply isn’t bad because it is childish. All calling it childish, or infantile, communicates is your own judgement.

Also; describing your judgement as ‘calling out’ - particularly when this is behaviour he has since admitted was poor, and has taken time out to address - just reads like you’re using the language of social justice to justify judgemental language.