I am a CPS social worker with a BS in Social Psychology. I often work with children who have disabilities. I would say that if you are only basing your suspicion of autism on the things you have listed above, I would not be the least suspicious.
It is very, very common in our society for little boys to play by making shooting or exploding noises. As for the posture when running, I have seen may children run that way and have not found it to be linked to any disability. Sometimes it is a child mimicking something they've seen, sometimes it is a "balance" thing, and sometimes it is just a reinforced behavior.
Every child is different and what you are calling "hyper-active" may not truly be "hyper-activity", after all he is only five. Be very careful of labels such as ADHD as I've found that it is wildly overdiagnosed. If you have much contact with children you will find that most of them are "hyper" and most of them have trouble paying attention. I would suggest that if you have major concerns you should take him to have a developmental evaluation.