Yes, you are intentionally harming yourself so that counts as self-injury.

However, that does not mean you will suffer a total relapse. There are different degrees of self-harm and it sounds like this was a pretty minute version for you. A nine month stretch without any is great so if I were you I'd shoot for none at all. Rather than seeing this as a failure, I would respond proactively. Evaluate your life recently to see why this may have happened and review your coping mechanisms. You may need to add new methods of stress relief to your repertoire or make other changes to your life to help you cope. It could be a sign of something else as well, but you would know better than I - after all, it's you. However, whatever it is, you don't want it getting worse so I would definitely evaluate. If you do and find that you just slipped a bit because you were in an abnormal situation with a lot of temptation, then you could start looking for ways to strengthen your resolve. None of us can say why it happened though, and I think that's really where you need to be looking.