Because DH is dyslexic so there's a higher chance, but also, he has no sense of blending, can't understand the concept of rhyme, it's a mystery to him what sound something begins with, he will just guess totally random letters, he will repeatedly misspell his sibling's name in a completely illogical way (e.g. Sam = ASM), when he asks me to spell words out for him, he doesn't know when it's the end of the word, he will keep asking "What letter next?"
I have an older child who also was not taught to read until he started school but he could do all of those things much more easily and younger. Without fully being able to read, he could do parts of it, recognise the first sound of a word, when we spelled things out he would mostly seem to know when it was the last letter because it would look right to him, etc. Even my 3yo can pick out rhymes. When we've played games with rhyme to try and help the 6yo, the 3yo gets it more easily.
We have had speech therapy assessments twice (once because of a slight speech delay, once because of a screening program for non-native speakers) and they have both picked up the difficulty with rhyming. The other suggestion is that it could be auditory processing disorder, but both speech therapists thought dyslexia was possible given the family history. They are not qualified to diagnose though.
Random stuff that has made me wonder too but not sure if it's connected or not - he follows Lego instructions upside down and back to front. Keeps forgetting that we read left to right and wants to read things like numbers or diagrams right to left. (e.g. 24 becomes forty-two).