It generally means the second one.
Cants in that sense can be pretty rich, and also act as a sort of lingual junction point in etymologies; through which words are borrowed from one language, change meaning, and then get absorbed into the general language of the area the cant is used in.
For example, we know that phoney comes from the Irish word fáinne ("ring") via English carnival cant fawny for the game of hoopla.
There are many other words were we know (or strongly suspect) that they came from a cant, but don't know any further. E.g. slum is from an American thieves' cant*, slang was found in several cants as the word for that cant itself, naff† was a term in the London LGBT and theatre cant Polari meaning "heterosexual" before it became a more general insult, and so on. Since we don't know the etymology of the word any further back than those cants, they're described as being "of cant origin".
*There's reason to suspect that slum comes from 's lom in Irish, but it's not as clear as the case of phoney so most people won't say more than "of cant origin"
†Naff became a general insult through Ronnie Barker suggesting it to the writers of the television show Porridge as a nonce word to use where the characters would more realistically use fuck, shit or other words that couldn't be used in a family-audience comedy show. Barker claimed he didn't take it from Polari, but since he couldn't recall quite how he thought of it, it seems likely he'd picked it up subconsciously from Polari; as a heterosexual comic actor he would have heard it from other actors and in it being used in the comedy show Round the Horne, but likely not have had great fluency in it himself.