Could someone please explain to me how this is possible

[animalguy]

Okay thanks for clearig that up for me. It was realy confusing when I noticed that.

 

[Camikaze]

I know this was the case in Civ IV, but I didn't think it was brought over for Civ V.

With this caveat:

1) the cost of the techs depends on how many civs you have met that already knows that knows the tech...

So it's not just how many others have researched the tech.