Would you say your son taught himself to read by spelling, or that the spelling was an outflow of his reading?
Hmmm... I believe that the *attempt* to spell developed a bit behind his reading attempts. He began to recognize words by sight (memorizing them, I suppose) at 11-12 months. However, it wasn't until a few months afterward that he began to realize that each letter in the alphabet had a sound. He would bring the letters to me when I was in the kitchen and ask what they 'said'. I would tell him and he would absorb that and move on to the next one. He did at first do things like put the letter "c" on one of his "cars" or the letter "d" on his "daddy." Once he knew all of those letters and their sounds, he began trying to spell words --phonetically.
I did wonder at one point if I should teach him phonics, but he was young and I felt a bit weird about that. I decided to let him figure it out on his own. His reading developed quickly once he began to figure out phonics. It was sometimes eerie how he decoded words. He did hit a period where he took his reading underground and wouldn't read to anyone. When he was four I would catch him reading the newspaper or sitting in his closet reading a book, but he did NOT want to read to anyone. We didn't press him at all. It wasn't until he was around five that he finally allowed us to again hear him read. Once he began to read to us, we knew he had been reading a lot all along. His reading was very advanced, but his spelling was STILL mostly phonetic.
We started homeschooling this past fall and with that he has finally shown an interest in correctly spelling words. If I ask a question, he will reply by spelling it. He's pulling it all together quickly. That's been how he learns --in huge, mind-boggling leaps.
I hope some of that might help you down the road as you watch yours grow and develop. I just want to encourage you once again to trust your own instincts. Arm yourself with knowledge and you will eventually come to a place of peace with it all, diagnosis or not.