It may not be ambiguous for you Bwatch but just because you have never issued a clearance to climb at a point, it doesn't mean that other controllers haven't issued such a clearance, and more to the point it doesn't mean that pilot hasn't previously recieved such a clearance. There is a possibillity of confusion on the part of the pilot and as such the pilot was right to question the clearance. Preferably the controller should have either cleared the aircraft to climb first, and then on recieving that readback, give the direct tracking clearance. In a procedural environment it is common to clear an aircraft once past a point that is known to be clear of a procedural area of lateral conflict with another track, to climb after that point. It is a common practice and is completely legal, and as such, a clearance of track direct to a point and climb, is poor phraseology.