Yes, it is. You are using player knowledge to achieve a desired result. Roleplaying, to me, is using character knowlege only. Our characters do not know that entering or existing a town during certain hours will prevent Vampire attacks. They don't even know Vampire attacks are possible. Only the player knows. And the reason the player knows is because they read these forums and they do research on the internet. That is the definition of meta-gaming.
That is not how I like to play. As I say, roleplaying, to me, is using character knowledge. It is playing as a character, one who in in fictional game world. That character knows nothing about the conditions that trigger attacks. Performing actions based on player knowledge of scripted events is not roleplaying.
Shmoe is right. This is not a player's fault. If a player plays Skyrim normally, if he or she truly roleplays, attacks will happen and NPCs will die. Many of my characters like to spend many nights in The Bannered Mare. When the exit the Bannered Mare in the morning they are likely to find that Vampires are attcking by the front gate. By the time my characters get there one or more NPCs (in my case, usually Adrianne Avenicci) are already dead. I'll be damned if I'm going to blame myself for that, or let anybody tell me her death is my fault.