Why do so many kids get diagnosed with autism these days?

I just saw a video of a supposedly autistic boy who saved his teacher's life by doing the heimlich maneuver. He was talkative and is a boy scout. My best friend when I was growing up had a sister with autism, and she could barely communicate. She would have frequent tantrums, had to go to a special school, and only talked sporadically through sign language. Now it seems like any kid with any kind of odd behavior or who doesn't quite fit in gets diagnosed with autism. This kid twitched a little but otherwise was fine. I was shy when I was a kid and I still stammer sometimes. Does that make me autistic? What about all the other socially awkward kids I hung out with?