difficulty drum scanning negatives

I sent some negatives and slides to drum scan to have the operator
claim that negatives show more grain in the final scan than slides. I
used 6x6 Fuji NPS 160, a film has low granularity rating. The other
film I used was E100G slide film. I find it hard to believe the
operator's claim. It seems that he is doing something wrong. What
could it be and how to get the best scan out of my negatives?
By the way, they use Crosfield drum scanners.

thanks
J