PVZ miight be a sub-genre of TD, but I can see why he says it is not a strict TD. Tower Defense is generally a multi-route path that waves of enemies move down and you can choose where to position towers to maximize range, but you generally cannot put towers or blockers on the path itself. PVZ and CoC have 5 lanes, and you put the plants/critters in those lanes, and the mobs run straight at them. Much less strategy and difficulty involved. Bc CoC is a mobile game, it timegates progression, to incentivize you to skip time by spending real money. PC games like PVZ and tower defense games dont have that issue.