This is 100% true, and poses another question - can you block the breath with something? A true area effect CrIg effect could just create a field of fire, including behind a shield wall or bit of protective rock. If he is really breathing out a jet, puff, or whatever, shouldn't you be able to, say, put a line of grogs with tower shields to block it from those standing beyond? (Well, if the shields can handle the heat, but that's a separate issue...)
If he is really just creating a 10x50 blaze, as the description rather implies, you'd need to step up the size by +3 total to get enough coverage, although then he'd actually be entitled to 20x50 or 10x100 because there's not any way mechanically to give half a size step at this point. Anyway, in some ways, it'd match the description a little better (more of a "torrent" that way, rather than a fireball), and I guess one could say that the breathed fire is rebounding, swirling around, super-heating the air, etc., so there's no blocking or avoiding it, no matter what the cover art for fantasy novels might imply.
If he's projecting a blast that could be blocked, I think a +1 size works but I think I'd probably require Aiming for that if I were SGing it, picking a specific 10 pace area for it to smack into. It'd still need to Penetrate, as it is magical fire, and I'd say anybody standing behind somebody else is reasonably well protected (until he uncorks a second blast, of course, as the ashes on the floor probably won't offer sufficient shelter), but that'd be the breaks for a lower level effect. I guess that's one way of reading "anybody in its path" - it doesn't say one way or another if that path can be intercepted along the way to its 50 pace extent.
I'm biased in this discussion in that I really don't care for the fact you can't block PoF with a shield despite it being a projectile. I tend to think of such spells as just causing the target to burst into flame, shield or nay, to satisfy the demands of my storytelling eye, or sometimes I picture them snaking around such attempts, guided by the magic. I suppose that's neither here nor there, but I tend to favor the blockable fireball type design because I like the idea of players going up against it being able to do more than resist or burn.