A major Indo-European contribution to the spread lactase persistence after all?

Ewen Callaway ("DNA data explosion lights up the Bronze Age: Population-scale studies suggest that migrants spread steppe language and technology."):

Ancient population genomics also offer insights on physical and physiological traits. Allentoft’s team found that the ability to digest milk into adulthood — nearly universal in northern Europeans today — was rare in Bronze Age Europeans, contradicting earlier claims that the trait helped early European farmers to gain calories from milk. Of the 101 sequenced individuals, the Yamnaya were most likely to have the DNA variation responsible for lactose tolerance, hinting that the steppe migrants might have eventually introduced the trait to Europe.

Related: More ancient DNA evidence of Indo-European mass migrations