most definitely genetics 110%. stable dogs dont need to be socialized to be stable. they are born that way.
my friend has a golden that sounds like your pup. in training the trainer tried to come up to her and she cowered and hid under a chair. once she saw someone riding a bike and immediately took off running the other way and there was no way of calling her back. scared of random things like a football. submissive peeing. just skittish by nature. my friend has slowly worked with her and now shes ok and can go places and more confident but she'll never be what i'd consider a stable dog.
she will never be a confident stable dog but right now you need to train her so that she isnt fear aggressive. i had a pup that was barking at a plastic bag blowing in the wind. i thought it was cute. well it was weak nerves and he grew up to be fear aggressive which is time consuming and a money pit trying to fix it
Can genetics be directed at just certain things? I've only dealt with adult rescue dogs before, so everything puppy is new to me. However, Loki is GREAT with unexpected things. First week we brought her home, the shelf in the pans cabinet broke, and she was standing right next to it. The loud sounds spooked her, she stumbled back, but there was no barking/whining/fearful actions after a ten second delay. Her ears were up, tail raised(in what I now know as her interested pose) and she was eying the cabinet with curiosity.
It spooked her for a bit, but she bounced back right away. Another thing--I had her out on a long lead while I was shoveling the drive way. Neighbor came out(close together houses), his door banged and she quickly alerted to the noise and him. He started to shovel, but she wasn't fearful/aggressive. Her ears were up, tail engaged, and she just watched him. I saw no fearful responses, and just her name called her back to me when she went to investigate, and she stayed by my side, but she did watch him for a little bit.
Perhaps I misconstrued that as her just being curious, and maybe she was fearful, but she showed no immediate signs or body language that she was anxious or fearful of the door closing, or my neighbor. In fact, it only took her a little bit of time to lose interest and start climbing our snow piles and rolling in them.