This is not arrogance, this is just smart strategy.
Think about it, if Harden somehow slips out of the top 5, you don't think at least one team in the early teens will happily pick him up even if they didn't personally worked him out? Just looking at the draft, I don't believe there's any way he fall past Toronto at #9. In other words, he's going to be in the lottery, the only question is where.
I don't think he has a promise because he'd have to stop his workout if he is to accept that promise but it does appear the Harden camp knows where his basement is and they're trying to establish his ceiling. Think of it as a student who is certain of being accepted to a top 15 ranked school and is now shooting for one of the top 5 ranked schools.