how do they do it?

Were any of them scientific? A couple got different MA techs and trade around or all five could be scientific. If several are on each track in the IA, they will soon all have the newly learned techs.

Did you have the ToE? If not it could have came in recently and two more tech one one shot.
 
Civs get a discount for trading amongst each either, the higher the difficulty level the bigger the discount they give each other. And they are notorious for trading any new tech researched. Though I'm surprised that 5 Civs traded, I normally see 2-3 Civs pulling ahead in techs, with the remainder trailing (normally the weak ones ripe for getting wiped out).

EDIT: Doh! vmxa beat me with the response :goodjob:
 
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