Now to me, that sounds like metagaming. Characters don't know that they are first level. They don't even know that they can't fight a dragon, or drive it off. Sure, it's dangerous, but people seeking adventure put themselves in danger all the time. Firefighters, police officers, soldiers, skydivers, etc. The 0-level militia men defending the village aren't taking into account their ability within the game to fight a dragon or an invading force.
But, look, everything in episode 1 is predicated on player choice. The PCs aren't punished by the adventure if they don't make the right choices. They can choose not to go into town; nobody thinks less of them for it and adventure provides for that option. They can choose not to go to the keep; the story is not dependent on their doing so, and the adventure provides for that option. Once in the keep, they can choose not to go out again; nobody forces them to or thinks less of them if they don't, and the adventure provides for that option. They can choose not to fight the dragon or the half-dragon; nobody thinks less of them for it and the adventure provides for that option.
Basically, the story opens with a force from the Cult of the Dragon attacking Greenest for loot. That's it. The characters choose where they go from there. They can wait until the attack is over or go in to try to help. If they choose the latter, they can choose to help villagers outside the keep or they can find safety themselves. If they choose to go to the keep, they can help there or go back out to help more villagers.
Sure, the game doesn't explicitly address what to do if the characters abandon Greenest altogether and go somewhere else, but by the same token it doesn't require that they go to Greenest to continue the story, so I'm hard pressed to see that as a failing. OTOH, it does provide Tyranny of Dragons special backgrounds, to help tie characters to the adventure if they want that. Any adventure needs the players to bite on the adventure hooks if they're going to play it. This particular adventure is in the extended adventure path mode, which means the players need to buy into the plot through line if they're going to play it. Within those constraints, I find Hoard of the Dragon Queen excellent for providing player and character choice.