If you had went out and bought some pot and started smoking it everyday. I would call it a relapse. But instead you're here and you're questioning your judgment. I think that says a lot. Some people are Black and White about this whole issue and that's fine with them. "To Thine Own Self Be True" is the phrase, you have to decide in your heart how you feel about this and what that decision will mean to your sobriety.
Will resetting your sobriety date to please to peanut gallery make you susceptible to going even further? If your sponsor already said he didn't count it as a relapse, I would go with what they were saying. That's why you have a sponsor in AA.
Remember "Progress not Perfection". As long as you can walk away from this experience having learned something, then I wouldn't beat myself senseless about it.
What's done is done, your next steps are most important and you seem to be moving in the right direction.