The alliterative aspects of anachronistic argot aren't always as apparent as the fact that you meant vocabulary; the terms are already in lexicons of victorian vernacular.
I'll take your word for it.
Since slang is defined as "a type of language that consists of words and phrases that are regarded as very informal, are more common in speech than writing, and are typically restricted to a particular context or group of people."
I doubt "cupids kettle drums" and "Got the morbs" were formal speech used by proper Victorians. Hence, he is correct in his use of "slang", and your assessment was inanely inapt, although amusingly alliterative.
'Twould appear you were away the day they handed out comprehension given your slips 'twixt cup and lip.
When I speak, I usually want the listener to understand what I said so I think Iβll abstain . Itβs bad enough that 50% of the people I work with are ESL without bringing in anachronistic argot