Fatcatsmaw, that all sounds very familiar, I'm afraid.... bright dyslexics use verbal memory and vocabulary to compensate in this way- it is a lot harder to guess a word from the context than simply to read it, but if you struggle to read then you learn to do it so it doesn't hold your reading back.
Capital letters throw things because if you are memorising the shape of the word it doesn't look like the same word with a capital- Again this is a much harder task (memorising the shape of every word) than just sounding the letters out, unless of course that is something that you can't do....
As to the spelling, building words and written work as text speak, that would all be things noticeable in my work at this age.
This is a bit controversial to say, and I don't mean to offend anyone, but in my honest experience a lot of teachers struggle to pick up on dyslexia in very bright children simply because they aren't behind in the way a teacher would expect- they are taught a model of dyslexia to look out for that includes the child missing targets and visibly struggling, which is not always the case.
I would take him to be tested, if it was me. It might be he needs a bit of directed teaching with understanding of what he can/can not perceive.