Re: Double Grading!
Back in the TKD days I somehow managed to get lifted past one complete belt rank, which at the time I thought was fantastic, and then got into stuff that my fundamentals weren't equipped to handle. It was an excellent challenge, and I am still grateful to my instructor for handling the situation in that way as I trained twice as hard on those fundamentals as I would have in order to correct the underlying mechanics than I may have if I just worked up the system from the bottom. In the end was I actually "ahead" on anything, I've no clue. Worked for the too-much testosterone mindset I had back in the late teens, however.
At our school now, we, like the above, aren't a big dojo (8-10) and we start folks t 5th kyu, and go from there. There's no double -grading, as I use the belt grades to break up the syllabus into digestible portions. We have had people come to us and be ready for a 5th kyu promo in 6 weeks, and for it to take as long as a year (not coming consistently was the issue).
Regardless, I think you are right about the background in karate and understanding the "idea" that movement is actually part and parcel of what the arts "do" to make them work gave you a leg up towards the double-promotion.
As Jun said, Congratulations, ranking up is always rewarding. it should be.