Could just be luck (well, genetics, probably) I guess. Maybe they'd have developed even faster if we'd used baby talk. One shitty thing about parenting is it's really hard to tell what helped, what hurt, and what didn't matter at all.
I would put a lot more of it to having (seemingly) engaged parents. Even a backwards strategy enacted by a loving parent who is consistently trying their best is likely to outperform the result that most can manage (owing to time/money/education/etc).
Genetics are a marginal element approaching none.
Compare a toddler living in a ghetto concrete jungle to one who takes daily strolls through Central Park or Suburbia. The enrichment of parents teaching about the trucks and the trees and the lady with a purple hat pays massive returns.
But, but... I didn't say anything about baby talk!!
The definition in that Wikipedia page is about something completely different: exaggerating intonation.
Baby talk (or CDS, child-directed speech) helps engage their attention and provides valuable feedback. Kids who experience less CDS develop language more slowly.
See https://en.wikipedia.org/wiki/Baby_talk
(I heard about this research a number of years ago. Although I must admit, now I wonder if it’s affected by the science reproducibility crisis!)