Fertility :: Sperms Motility Lower, But Swims Faster?

My husband(30) and I(29) are being evaluated for infertility. My husband was told his semen analysis results over the phone, but we won't be seeing our doctor for another couple of weeks.

The only problem in his analysis was that his motility was found to be slightly lower than average, however the doctor said his sperm was found to swim faster than average, and he was also found to have better than average morphology, so he was told not to worry because these two 'better than average' factors compensate for his slightly low motility.(Volume and sperm count were in the normal range).

We are not sure we understand how motility can be slightly low on the one hand, but sperm swim faster than average on the other hand. How is that not contradictory? Should we be reassured, or slightly concerned about the low motility?

(If it is of any importance, his specimen was collected in a lab through masturbation after 3 days of abstinence. Per my husband, much worse conditions than intercourse).