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.