Boys develop coarse motor skills first, then fine motor skills, for girls it's the other way around. Which also means that girls are quite good at sitting still in primary school, boys, without getting tired out in recess, very much aren't. Cue "behavioural issues".

Lego did control for everything that could be controlled. They're the OG "our toys are for everyone" company. They thought that their stuff was gender neutral, that stores and parents, society, were the problem, but had to admit that, no, kids actually do have, statistically speaking, different play preferences. Their female set designers didn't catch it because they were not kids, any more.

And "no hormones to speak of" MF if there were no hormones involved male karyotypes would develop female.