Faster leveling than everyone else

Just now I was playing an ARAM and everyone was doing the normal poke thing, still level 3, when the enemy Hecarim roared out of the bush- at level 5. Whole team was going "wth?" Later he dinged level 6 moments before the rest of his team turned level 5.

Is that even possible, even with exp runes/masteries? I checked his rune/mastery pages and it didn't seem like he had any exp dedicated ones set up at all.