I don't know, I typed a long response but I can't really express what I want to say. I didn't diagnose you.
The ability to concentrate very intensively for hours on difficult material is not a common trait (in the population at large).
Feeling 'bored' enough that you avoid going to class despite all the extra work this implies, and the grade implications, is not a common trait (among people who hope to go to a good graduate school).
However, for someone with ADD, both hyperfocusing on things they find very interesting, and avoiding situations that require sustained attention on anything that they don't find especially interesting would be almost a given. More then a given, these are symptoms.
Finally, something can be a valid explanation of why an action was the right one, but still be a rationalization if it doesn't take into account the true motives behind the decision to take the action. There is certainly a school of thought that says basically all explanations (both before and after a decision) are at least in part rationalizations, since we do not know our true motivations at all.
So I believe you 100% when you say you "used your time to your best advantage", but I believe you came to this course of action, at least partly, to give yourself an excuse for avoiding unpleasant feelings of boredom, even though it is clearly expected for students to attend class.
Finally, you continually state it as though you had to choose one, read up on research or go to classes you found boring.
Here is why your explanation doesn't convince me:
Classes take up 12-16 hours per week, so skipping them gives you 12-16 hours of extra time studying important things. Awesome! That is a good thing, I'm not being sarcastic.
Add commute time, meals on campus, conversations and other crap, now we are at 14-28 hours per week, which is sizable.
However, sometimes you can't skip a class, do to tests or turning in papers, so subtract a few hours per week from your 'time gained'. Maybe we are at 10-24 hours per week gained now. (Guessing around 4 hours combined of class time + overhead of commuting etc that is unavoidable per week)
In most classes you could sit and read whatever you want the entire time, while still benefiting from being there and recognized by the professor (good if you need anything from him later, also this unfairly effects your grade) and are aware of homework, readings, and at least partially of discussions and what the professor cares about. You may also find that you are more interested than you thought you were, and the class is no longer considered 'wasted time'. Once you take away time 'reading what you want' in the lecture, and 'unexpected interest in subject' time, maybe you are at 2-18 hours gained now. (Guessing around 6-8 hours per week can be spent reading what you want, unexpected interest in a subject cannot be estimated.)
Now subtract any commute time you do regardless of class attendance. For example, if you are a commuter and you have to attend one class, go to the library, or talk to a professor, you have to do the full commute regardless of class attendance. I estimated between 1 and 8 hours of commuting time per week. If you end up going to campus every day, or you live on or near the campus anyway, you are down to between 0 and 10 hours of 'time wasted' per week. You cannot say that even the maximum possible 10 hours gained per week is some kind of deal breaker to studying on your own.
So that is my thought process when I read your initial post. Then I thought, if this person isn't really gaining much time to study by skipping class, why do they feel so strongly about it?
So an unconvincing explanation of why, a statement that those classes are 'boring', a statement that if you had to attend those classes you probably would have quit school (they must be pretty unpleasant to you!) all adds up a high likelihood of ADD to me. Your analysis may be different, but given the limited facts I have available I am convinced. This is not a diagnosis, merely a statement of how it seems to me.