I believe it is. I've explained before elsewhere why I think this is the case, and those reasons include the name making sense for some sort of career prologue, the fact that there is a very obvious nonfunctional monetary system in the campaign, and the fact that it really does just feel like a complete, albeit short game with cutscenes and everything.
Rocky Start was a preview of what career mode was planned to look like back then, iirc. Remember that Rocky Start came out way back in 2016, and the idyllic image of what a BeamNG career looks like has probably shifted since then.
That's right. Rocky Start was our first research into career mode. But there has been other implementations in the meantime (not public though), and none of them necessarily represent what the final Career mode will look like.