quite tricky question! I think mine is definitely partly genetic/physical but I only know one of my cousins who used to seem to have social anxiety/phobia but after I think he went on medication or didn't have it anymore and on my dad's side, they were called "weird" or eccentric but not mentally ill, we don't know of that side. I only for sure know on my mom's side that everyone is okay but I know my grandma gets anxious/nervous when family member's aren't doing well. My mom is the same as her mom (grandma) but there's no one else on her side that has "social anxiety/phobia".
I also didn't eat particularly nutritious food growing up. We were in a poor neighborhood and ate hamburgers, hot dogs, beef patties, cereal with a lot of sugar in it and outside food so that wouldn't be good for the developing brain like I did not eat whole foods, no sugar, Omega fish oil so I don't have good neurotransmitters anyway.
Also, how I was brought up and how the world was like didn't help. I didn't know how to defend if I got a bad hair cut and then others didn't like me, how to defend if others didn't like me and what mattered the most was if I was a good person and then I don't have to care if others don't like me for any other reason and I didn't have God in my life to always meet the right people and be sure I have all my needs met and that unrighteous enemies will get punished and to think positively and the right and not "worldly" or crooked or common ways of the worldly thinking and ways so I was a teenager and developed social anxiety/phobia and after I got it, I couldn't change it, no matter how I thought or were to go counselling so I think it was just genetic/physical, something wrong with my neurotransmitters, but I don't know if I was brought up in a very different and spiritual family and they taught me the right, positive way to think if I would've still got social anxiety/phobia so your question is tricky.
However, after I got treatment from my naturopathic doctor with vitamins, I basically have no more social anxiety/phobia so that shows that my neurotransmitters aren't good/strong and that I need/depend on medicine/medication even if it's natural, to treat it and calm things down or whatever it is that helped me. So I don't know how to answer this question without writing all this. I am a bit confused.