I repotted my snake plant this morning because one of the leaves was soft and turning yellow. When I took it out of the soil, the roots were very dry. Does that mean it wasn't getting enough water.

Was the soil dry too?

They will naturally lose older leaves but soft and yellow and dry roots don't usually go together. Has the leaf recently yellowed? Was the compost dry? If you removed that leaf and any associated softness around the roots I would give the plant a thorough watering and then leave it until new roots have had a chance to grow. What did the remaining roots look like?

Yes, the soil was dry because I was told not to water often.

How often do you water and what kind of light does it get?

Although overwatering is the easiest way to kill houseplants, very few will thrive while being kept too dry. I grow a lot of Sansevierias and for the most part they do need a fair amount of water. I give them a thorough soaking and then leave them until the top inch or so of compost feels dry. Where they are situated and the time of year also impacts on how much water they need.