In most models, falling child mortality is responsible for about half of the life expectancy growth in the past 150 years. But the other half is indeed longer lives at all age groups[1]. So I don’t think this is a lie, or even misleading (since the author made no claim about non-childhood causes being disproportionate).
[1]: https://ourworldindata.org/its-not-just-about-child-mortalit...