And what about when he was at 8k IPH, 12k IPH?
I'd bet you a grand he exploits. The legit massive gold buyers I know always buy gems as well for Gold Mines, Corruption Towers, Events, etc. Why not you are loaded and have tons of real money to spend and gems are fun.
The exploiters always have zero gem buildings and gem units. They're happy with unlimited gold and don't want to spend a real dime at all; theres no need too. And if they get busted and banned, they haven't lost a penny on the game.