I don't necessarily agree. My understanding of anarchy is that it's based upon voluntary association, but in this instance as an example, voluntarily associating oneself with anarchist philosophy by labeling oneself an anarchist. To say a person doesn't understand anarchy because they label themselves an anarchist is to claim that you understand anarchy better than they do, which sound kind of oxymoron(ish) when considering the original argument you make.

I'm sure there are many people out there who claim to be anarchist but do not abide by anarchist principles, but to use your argument as a rule of thumb would be logically fallible.