The tooltip for Guardian Angel (GA) says
Passive Unique: Revives your champion upon death, restoring 750
health and 375 mana. 5 minute cooldown.
But as far as I neither Kill or Death counter are increased for the involved champions nor any gold is given to the "killer" when the passive of GA triggers.
Since stacks on Stack-Items (e.g. Bloothirster) are lost upon death, I wonder if being revived from GA's effect counts as a death or not.
The lol.wikia.com article on Death states it as Ways to prevent death when reaching zero health
which confuses me even more.
Best Answer
The League Wikia has a page explaining "Removal of stacks, buffs or effects".
In the "Ways to prevent death when reaching zero health" section,
"Prevent death" should be interpreted literally. At 0 HP or less, Guardian Angel triggers and automatically brings your champion to 750 HP. Even though there is a delay for the stasis animation where the champion is untargetable and invulnerable, the champion did not die.
But I encourage somebody to record a video because that's the most convincing evidence.