Yes, it does have a heredity component, though it's not well understood yet.
School should support his diagnosis, though in practice a lot can depend on individual schools, I think. Did they have any role in suggesting the assessment? Or did they flag up problems? How did it come about?
The school will have a SENCO, who is the person who heads up everything to do with special needs such as dyslexia. They ought to be able to reassure you, if they're good, and they ought to be able to look through the assessment report (which you may not have yet?) and, hopefully, explain to you what it's found.
Dyslexia as a term covers quite a variety of experiences, so every dyslexic is different. But there are characteristic patterns, such as difficulties with reading, writing and spelling, or perhaps with organisation, telling time, understanding left and right - does any of that sound familiar?
There are loads of people on here who will be able to help (much better than me!), but if you can say more about your DS, it'll be easier, as it's hard to know without knowing him. What I do know is that if he's got to this point, he must have been working incredibly hard, and he should be really proud of himself. Dyslexia can be a real advantage (even when it doesn't feel like it), and he's welcome to the club. 