The abstract of the orginal study states "Growing up with home libraries boosts adult skills in these areas beyond the benefits accrued from parental education or own educational or occupational attainment."
https://www.sciencedirect.com/scienc...-research-data
Of course having a 'home library' is a likely indicator of a family that values reading and in fact the researcher are using the 'home library' as a indicator of 'book-oriented socialization' (what ever that means).