[Dan Mezick]

Check raise is not really 100% aggressive. It is often a probing manuever designed to see where you are (typically after the flop) and can accomplish certain other goals, like getting a free card (etc). The check raise is often used as a semi-defensive play early in the hand, such as when you hold 2nd pair after the flop and need to better define your opponents likely holding.

Consequently check-raising may not really apply here. As the final point, I notice that Doyle, arguably the definitive aggressive player, states in SS1.0 that he 'does not like' the check-raise, mainly because the opponent can GET AWAY when you use it.

Is the check-raise 100% indicative of pure aggression?

Probably not.