My guess is by "arc," they mean story cycle. If that's the case... Holy crap!
They've said for a while it's 3 cycles. Misleading headline, though. Clickbait, I guess, since the first thing they talk about is how its not the final "arc" at all.
Yeah, a lot of articles seem to like giving titles to Mignola's interviews that imply the Hellboy Universe's end is imminent. The reality is there's a LOT more to come.
Well, more five or six years from BPRD! (enough to Mike finish Hellboy In Hell too? haha)
I imagine that the end from Hell on Earth will be the defeat from the Black Flame... what do you guys think?