It is very important that you see a developmental pediatrician. They are the only ones who can tell you what is going on. I might also talk to them about the possibility of cerebral palsy.
Honestly, no one can answer that on the internet. Your child needs an evaluation by a professional. Some kids with motor issues such as not meeting milestones of sitting up have dyspraxia which can be associated with autism or sensory integration disorder or on its own,. No one here can say for certain. Your child could also just be a late bloomer. My son walked/ran at 9 months . . . but this actually turned out to be a sign of sensory integration disorder when I thought it meant he was advanced at the time. You just never know,.
Talk to your pediatrician who will probably refer you to a specialist. good luck