Blessed mommy, your ds sounds very much like my ds (who has DCD and is dysgraphic and who has had hints of stealth dyslexia, definitely reads from context). FWIW I have a dd who also struggles tremendously with reading but has a different diagnosis. I'm sorry I'm in a huge hurry this morning, so this will be very brief - I hope it makes sense!
Should we tell him he is dyslexic so that he can better understand why he struggles with spelling & writing? That it is just his brain is wired differently? My fear is that it will hurt his self-esteem and confidence around reading.
Dyslexia is a confusing word, even for me - there is the classical definition of dyslexia, the Eides' definition, and then there are kids like my dd who have a different challenge that can tremendously impact their ability to read fluently. So - jmo - I wouldn't use the word dyslexia at this point, but would instead let your ds know that the testing he had revealed he has certain types of challenges (explain the challenges) relative to other children (and also let him know what the testing revealed about his strengths). Your ds already feels different than other kids, and he's already comparing his performance to other kids - this is absolutely normal, and it's where kids with a learning challenge start to really have their self esteem impacted in a big way - so it's important to explain what you know about his challenges to him (from the testing and your observations) and also to let him know what you (and others) are going to do to support him and help him with those challenges.
When our ds was feeling overwhelmed with his challenges or sad about them, I found it was helpful to find stories online of adults who'd struggled with either dyslexia and dysgraphia and read them to him - there are a lot of brief bios online of people to choose from

I did use the word "dysgraphia" with my ds and it definitely helped him have a name to associate the challenge with. I've used the word "dyslexia" with my dd too... yet I've found that to be a bit more complicated. She has a dyslexia diagnosis, but she doesn't have the traditional dyslexia profile, so it's not a word that works well in advocating for her at school (I am still her primary advocate since she is still young - whereas my ds is in high school now and he totally owns his diagnosis and uses the words to explain it). When I use the word "dyslexia" teachers/professionals/etc expect me to be talking about traditional dyslexia, so instead I explain that she has a challenge with associative memory which makes it difficult for her to retain the associations between sight and symbols, which in turn makes reading difficult (how's that for a mouthful lol!).
Anyway, I tried not to overemphasize the word dyslexia with my dd simply to avoid having her use it and having adults who she talks to become confused by the term. I'm not sure yet how this will all evolve as she grows older, but for now it's worked to simply talk about how reading is difficult for her.
I have to run, and of course I have more to say - sorry if the above is a bit jumbled.
I know how heavy it can feel the first time you have those official results, but it will also be so very helpful moving forward -
Best wishes,
polarbear