AP Xin Zhao can solo inhibitor turrets without minions

Exactly as the title says. I played against a Xin Zhao in teambuilder a few minutes ago, and he built nearly full AP. Lich Bane, Nashor's Tooth, Rabadon's Deathcap, Hextech Revolver and Berserker Greaves. He didn't build any resistances. He just walked up to turrets while the wave was at his own, and took them down. He'd be at full health afterwards. There was no chance in outdueling him or even slowing him down without ignite, because he simply healed so much. Summoners were ignite and flash, so it wasn't like he was using heal at the last second or anything.