Is this still griefing?

Is not finishing the nexus in a match (i.e. letting winions take the entire health bar sort of thing) still considered griefing? It's becoming more and more popular (or at least seems to be) in ARAM matches and it's more frustrating than anything else I've seen/read. My own team just wanted to do it (or at least one did, others didn't seem to be hurrying to finish), but still finished it off b/c it was pretty one-sided (to the point the enemy team even asked us to finish).

When I asked the one who said he didn't want to end, it basically boiled down to the new XP system and getting more XP because the match went on longer... I'm sure that's just an excuse, but even so, it could be seen as Riot justifying dragging out matches like this.