[Commonmind]

Though it's definitely plausible, you have to consider the source. Harry's the one making the comment - in a speculating manner, as if to say the reason Bane made the statement might have been because it was written in the stars. That's not to say that it was, but only that Harry was remarking on their particular breed's mentality and may be taking a stab at it. If the Centaurs are forbidden to meddle in the fates of men, it would be considered taboo for Firenze to have helped Harry, despite his death being foreseen or not.

We can't rule it out, although it would definitely have been more concrete if it had come from one of the Centaurs.