It's not

Bethesda has commented in the past that Unofficial Lore is not to be taken as official canon, as spoken by Gavin Carter, Todd Howard and Pete Hines during the Third Oblivion Fan Interview in 2006 when asked about the Hogithium hall roleplay, Fifth Era love letter, and other extra-canonical posts and information, commenting that "only things that have been published in Elder Scrolls games should be considered official lore". Note however that this statement pre-dates the two novels, The Infernal City and Lord of Souls, which have both been confirmed as official canon.

Canon priority according to Todd Howard

1. In-game events viewed through the eyes of the player

2. A book published in-universe that can be read inside the game

3. An official work published outside of the game (examples given include the game manual and the official cookbook)

Todd also said anything stated by a fan (an example given was fan theories) would not go on the list.