I suspect "mainly" in this case means something along the lines "60% of poorly educated people voted leave, 40% of highly educated did", not "everyone poorly educated voted Leave, everyone highly educated voted Remain". That 83% figure comes just from "2000 scientist working in EU", not everyone who is considered highly educated.
Plus, some of the older folk didn't even had opportunity for what is considered "highly educated" nowdays; it doesn't mean they are uninformed however or lack experience.