Well the range the person at the shop quote is correct in a very general sence but I highly doubt that the top gear is going to be very tall. From a quick look at the specs for the curve d3 I found it shows a 46t chain ring up front and at best it might have a 16t in back coupled with the 16" wheels and the 3 speed hub you would get a 34 to 61 gear inch range so this baby would not exactly be built for speed. Most of the 6 or 7 speed derailleur systems I have seen have 14-28t freewheels out back which are usually coupled with a 52t chainring and on a 20" wheeled bike that yeilds a 37 to 74 gear inch range. Now I have made a number of assumptions and I would need more information from which bike you were directly comparing them to but my conclusions would be this:

A. The Curve D3 is geared pretty low so it would be suited to climb hills but in the flat anyone would probably be in the highest gear.

B. It is very comparable to a 7 speed system but it appears to be slightly lower gearing.

C. With a 34 to 60 gear inch range this bike is not at all comparable to a typical road bike gearing range which is in the 28 to 120 gear inch range.

Side note: not sure if you know but the smaller the gear inch number the easier the gear.