I think the Dark Knight flicks made a good choice in making it seem like all the origin stories were just stories joker made up for fun.
This was definitely the real Joker though. But obvioisly a different origin story - though not necessarily because there might always be a vat of acid in his future.
And lets be honest this origin story rocked.
The Nolan movies didn't have Joker give different versions of his origin story. He gave different versions of how he got the scars, and yeah, that was a brilliant little gimmick among many in that trilogy. How he became the Joker was never actually addressed, though.
Unless they change it in the sequel, this wasn't the super villain Joker. He was a depressed ordinary shmo who inspired future lunatics, one of which became the real Joker. Now I have to rewatch the ending to recall why I came away with that. For now, I just remember a bunch of copycats rioting in the city.
And nah, the origin story didn't rock. It was a great take on how those marginalized by society could lose it, but I'd almost rather they have created a brand new psycho personal than to pull the Joker into it. I mean, the Joker's whole shtick, consistently through every single era and variation in the comics (AND movies - Nicholson, Ledger, Cesar fucking Romero!), is that this is a guy having FUN committing crimes and killing. He's literally never sad, even when getting his face punched in (just like when Ledger was laughing in the interrogation room while Bats beat the shit out of him). On every level open to reasonable interpretation, this is a different guy. There's no way that Joaquin's guy turns into Ledger's guy.