No, but having certain levels does suggest it according to WADA guidelines. Again, not anything to do with the NSAC, really, in any sport that is subject to the worldwide overarching anti-doping organization, his levels strongly suggest that he was influenced by the active ingredients in marijuana in competition. Now I don't know how to interpret the level of certainty that those levels suggest and I'd suggest neither are you.
Perhaps marijuana should not be tested for in competition, at all. I recall Dick Pound, the former head of WADA who is interviewed a fair amount up here in Canada (as he is Canadian), suggested that there are many within WADA and involved in drug testing in sport that don't feel particularly strongly about marijuana being a banned substance in or out of competition, though, there is a sizable contingent that see it as a substance that puts those who are under the influence of its active ingredients at undue risk in competition. At present, the official position of WADA is that it presents undue risk to athletes competing under it and as a result they set those levels so as to have the best chance of catching those who are under the influence in competition while avoiding sanctioning those who were under the influence only outside of competition. The problem about your reasoning that the levels don't ensure absolute certainty that he was under the influence during competition is that the same reasoning could conceivably be used for certain stimulants that are banned in competition, but I don't think anyone would want to be erring on the side of doubt with regards to stimulants in competition. As long as WADA determines it should be banned (which is debatable, certainly), it would seem that the testing they use is reasonable even if it doesn't prove with absolute certainty that he was necessarily under the influence during competition (again, I'm not sure if his extremely high levels more or less confirm that he was under the influence, anyway, or the effectiveness of the 150 ng/ml threshold in determining whether the athlete was under the influence in competition).