Introverts can sometimes lean toward avoidant relationship patterns, and childhood experiences may explain part of why those tendencies form.
Introversion and avoidant relationship style are not the same thing, but I can see why they sometimes overlap. Introverts generally need more space and lower stimulation, while avoidant people often protect themselves by creating emotional distance.
That overlap can become stronger when childhood experiences reward self-containment. If a child learns early that emotional needs are inconvenient, dismissed, or unsafe, independence can become more than a preference. It can become a strategy.
In that sense, a lot of adult behavior does seem linked to childhood, even if not fully determined by it. We build adaptations early, and then later we mistake those adaptations for personality. Sometimes they are personality, and sometimes they are just old survival patterns wearing a familiar face.