Go with your gut instincts!
There is an awful lot of misinformation out there on autism/Aspergers. Even the “professionals” are too often beating down the wrong path.
Really the best place for autism information is from autistic individuals.
As you have noticed, your son has figured out many things on his own. He just didn’t have the tools nor the understanding of possible tools to use besides the iPad one informing you of his basic needs and desires.
For me, the voice that I hear in my head when I speak is the same as when I was a child. But I know from hearing recordings of it, it is very different than my perception. And yes, I am not big on talking.
My take is that too many autism parents get fixated “on finding the cure” instead of working with the child identifying their skills and abilities as they grow. In some ways the iPad is a boon but also a curse unless the software app can learn and adjust itself to doing more complex needs.
Now that you have found the ‘key’, enjoy your adventures in communication and learning with your son. You will find a fascinating brain inside his head.