Yes, it's "dragon or above". It could possibly have been god. The final attack could've wiped out humanity if what Boros said was true. We'll never know. In the perspective of the hero association and other characters, they wouldn't know as well until something truly happened indicative of it, but hasn't wiped out humanity yet. It'd probably also be hero association's best interest not to cause unnecessary panic if they're not sure anyways.
The author is very clever in this regards: making something for an endless discussion amongst the fan base. I believe "dragon or above" was the statement from the author himself, not within the series. If he straight out revealed "Boros is god level", he'd be instantly destroying so much discussions/debates/fights within the fan base, and that certainly wouldn't have been beneficial for the manga and himself. But if he said "Boros is dragon level" it would've limited Boros' ability, and what Boros said himself about the final roaring cannon attack would've been a lie.
