Why does my dog bark at random noises but not fireworks?!

[LoveUsed]

Had our rescue for 4 weeks now. He’s a China jack apparently (although we just call him a terrier cross!)
He’s very vocal as you would expect from a terrier. He barks when the door goes or if he’s in the garden and he can hear someone outside the fence etc. He also barks if he can hear someone shutting a car door about ten miles away, I always think ‘oh ddog just let people live their lives’ 😂
I was really worried about fireworks coming up, but some weirdo had some fireworks going off last night and ddog just carried on wandering around, chewing on his chew etc.
Absolutely not complaining! Just wondering why. Obviously might be the frequency, but just feels so strange.
He also suffers with anxiety (separation and otherwise) so thought fireworks would definitely freak him out!

Perhaps he previously lived somewhere where loud bangs were normal? There is a study that shows dogs born in later summer/early autumn are less likely to be scared of fireworks - presumably because they are more likely to have heard them and got used to them during their formative puppy weeks. Whereas dogs born in winter would be several months old before bonfire night came around for the first time.