It can be. I have friend who rocks in his chair, bounces on the sofa, in his wheel chair. He is in his 20s.
It doesn't mean that anything goes. If he rocks quite a lot in his wheel chair or on a wooden chair that can be quite dangerous, especially if over excited (either through happiness or sadness). I get him to sit back, although a certain amount doesn't matter just when it gets out of hand.
Just becuase slimming can help, doesn't mean it always help. It depend on what frame of mind that he is in. Some types of stimming helps when he is distressed like his needs, but not rocking this will further escalate into meltdown. I will try to redirect that to getting him up so he can walk (he has some mobility). he has damaged furniture and his wheelchair from meltdowns, so sometime it better to get him up, get him to focus on his breathing.
Obviously we try to find out what the problem is when appropriate.
I have found myslef rocking myself, but mostly I've paced.