In my experience, yes, it's always been related to anal glands, though I'm sure there could be other causes. One of my family dogs scooted all the time and my mom would have to express his anal glands (or take him to the vet). Watson scooted once in the house and expressed his anal glands while he did it (thank goodness it was in the basement!)
Watson scoots if he has a messy poop and thinks he needs to clean himself up by scooting in the dirt. It's hilarious.