Something that is a fact, is true, not everyone is expected to know it, but you shouldn't express an extreme surprise or doubt when you learn it.
The comment "Didn't know that code was measured in units of 'strengt'" sounds like the author is casting a doubt on the asker's assertion. So, the asker just answers in a tongue-in-cheek manner playing a pun on the commenter's nickname; purposely misinterpreting a cynical statement as a genuinely informative one, in order to sound playful and not seriously admonishing.
The tongue-in-cheek meaning is "The fact you didn't know is irrelevant to the answer".
The literal, intended meaning is "You have a right not to know that fact, but you could have checked, and you'd know there is nothing wrong with that"
Note it's not some idiom, it's just a situational play with words.