Electrodermal activity is an index of sympathetic activation and a skin conductance response can occur in many situations. It is therefore a very general response and can arise as a result of stimulus novelty or “significance” (whether you want to call this an affective response is up to you but it seems very different from common sense notions of what an emotion is).
You can however measure phasic responses specific to a stimulus in the sense that even a single presentation can be followed by a skin conductance “spike”. The shape of the response will however not be specific to a class of stimulus or narrowly defined content (there is no obvious characteristic “fear” or “happiness” signature, no “audio” or “visual” skin conductance response).
There are some attempts to discriminate positive from negative emotions based on skin conductance and also quite a lot of research using machine learning techniques to classify emotional responses based on physiological measurement but usually not on a single signal, and without much success for electrodermal activity alone.
Skin conductance is often interpreted as some sort of physiological arousal but that's a notion Wolfram Boucsein would probably have considered too simplistic. I don't think you need to over-analyze a single sentence to find an answer to your question, it should be quite clear from the whole book and, implicitly, from the fact that Boucsein did not discuss patterns of skin conductance responses associated with discrete emotions (which he would have if well-established results on this existed).
If you dig into the psycholophysiological literature, you will find that sophisticated approaches try to disentangle the activation of various part of the autonomic nervous system and deal with things like the defense or orientation response, preparedness to conditioning, fight-or-flight, etc. None of this maps neatly to subjective/expressive emotion categories like “fear” or “anger”.
Regarding the Q-Sensor, I have never actually used it but I have read a few papers and seen work from Rosalind Picard's lab at conferences and the like and I was under the impression that a big part of this research was concerned with skin conductance level, not responses (i.e. tonic responses, things like being relaxed or excited by an activity over a period of several minutes, but not phasic responses to a single picture or audio clip). If you follow Boucsein, it's not even clear you could get a clean measure of phasic responses with a sensor that's not firmly attached to the body on one of the spots with many sweat glands (palm of the hand or foot).
Some other references:
Cacioppo, J. T., Klein, D. J., Berntson, G. G., & Hatfield, E. (1993). The Psychophysiology of Emotion. In M. Lewis & J. M. Haviland (Eds.) Handbook of Emotions (pp. 119-142). New York: The Guilford Press.
There is a chapter on the topic in every edition of the Handbook with a slightly different constellation of authors each time but I don't have the references at hand. The one from the second edition (2000) contains a meta-analysis of studies on the discrimination between discrete emotions through physiology.
Dawson, M. E., Schell, A. M., & Filion, D. L. (1990). The Electrodermal System. In J. T. Cacioppo, L. G. Tassinary (Eds.) Principles of psychophysiology: Physical, social, and inferential elements (pp. 295-324). New York: Cambridge University Press.
Again, the chapter has been updated in later editions of the book (published under the title Handbook of psychophysiology starting with the second edition) and is worth checking out.