Everyone will have an opinion on your parenting whether your son is quiet or loud, hyperactive or laidback, or whatever combination of characteristics he has. We all think we know more than anyone else, whether we are parents ourselves or not. You shouldn't have to worry about other people's judgement if you are doing the best you can. I know it's easier said than done, but I just want to reassure you that if people are judging your parenting, it is probably because they want to deflect their own concerns about their own parenting, because they will have them. It always baffles me when people stare/judge children being overexcited/hyperactive, because that is the natural state of being a child, especially when they're at the park.
You don't need to feel guilty about describing his character and behaviour, because there isn't anything wrong with it. Even if he is assessed and is diagnosed with a learning difficulty or disability, that still doesn't mean there is anything wrong with him. I would encourage you to read as much as you can about the social model of disability, because in the early stages of assessment/diagnosis, it is very easy for parents to blame themselves and feel as if they have done something to 'cause' their child to be disabled or have a special need. It is helpful to avoid reading things from the perspective of the medical model of disability (that SEN and disability are "deficits" rather than just a natural variation in the human brain). Of course, that is not to minimise the challenges that come with being disabled or having SEN.
The positives that I've got from your post is that your son is incredibly bright, he's in nursery yet he can already spell his name and some other words, his counting is amazing, he has lots of energy and excitement, and is a lovely affectionate boy.
It is easy at this stage to worry about the future and to think about the challenges that lie ahead if he is diagnosed with a learning difficulty. However, there is no way to know what life might hold for him in the same way you don't know what life might hold for any child. You just do the best that you can.
I have worked with young disabled people for the last six years and some of them will need care for the rest of their lives, but I've also seen some of them exceed everyone's expectations by going to college, gaining employment, etc. There is a young girl I began working with 6 years ago and when I met her, she had very high support needs, very high anxiety and needed 1:1 support. She now travels by train independently, studies at a mainstream college and regularly meets up with friends in town to do regular teenage things. My own sister was very delayed in her speech and learning, and we were told she would need full time care for the rest of her life. She is now at university.
You don't know what the future holds, so just take it one day at time. Read a lot if you find that helps, but make sure you don't just read stuff written by doctors and psychologists. Read things and watch videos by people with LDD, whether that be ADHD, autism, cerebral palsy, dyspraxia, whatever. Even if it's not your son's possible future diagnosis (if he is diagnosed with something), watch it anyway and continue to remind yourself that, if he has a learning difficulty, it is not something you caused, it is just part of who he is.