Autism isn't extroversion or introversion. Extroversion and Introversion are about how you expend/gain energy in an interaction. Extroverts feed off social interaction, introverts get drained by people bombarding their senses. As a result, introverts can be withdrawn and can be seen as awkward and aloof, but it's not because we're biologically incapable of interaction, we're out of practice because we're not used to it because we're not as interested in it as extroverts and less likely to engage in it. People with autism have an inability to communicate or recognize the outside world as we do. Where introverts choose to be locked inside their mind to recharge, people with autism frequently feel frustration with not being able to express themselves or comprehend the world around them. There is a disconnect between sensory and logical development, and they can be aware of this, though sometimes the sheer breakdown of communication inhibits that kind of understanding - sometimes there's just no way to communicate it to them.
An autistic person may be shy, withdrawn, and internally focused, but that's not because of whether or not socializing charges or drains them - it's because they're biologically forced inside and kept from reaching out. They may get tired from social interaction, but that's not necessarily because of people bombarding their senses, it's because of their own struggle to communicate with you (the source of the draining is different). Imagine trying to speak, but your mouth just won't make the words - or having a thought, but there's only this sound coming to mind and it's the same one over and over again, and so you keep making that noise hoping to get someone to pay attention and understand what you need, or seeing someone in pain and not being able to understand why they're crying, because faces and expressions just don't make sense to you. You might not be able to express it yourself or your brain's wired to express it in ways we don't comprehend. Imagine how you would develop if you couldn't communicate a single complex thought or complicated feeling you had. The horrifying thing about autism is that frequently they have the same inner world we do, and no way to show it. Obviously there's degrees of it and that would be an extreme, but people with autism are extremely brave and amazing to get to know and deserve to be understood.