You will tend to win more money at showdown than you do overall - hopefully you're going to showdown with your better hands. Your overall win includes all the small amounts that you bet before folding.
If you win a few pots at high limit but lose a lot at low limit then your BB and money win rates can be very different.
How many hands did you import?
How long did it take?
Did you use manual import or auto import, or the setup wizard?
Auto Import isn't designed for large scale imports like that - you should use Manual Import or File > Setup Wizard.
Auto Import is only designed to import new hands while you're playing.