This strongly suggests they had checked in luggage and simply didn't want to pay even more just to bring some in the cabin. A flight is not like a taxi ride, you're all but guaranteed you need luggage. So I think the cause-effect relationship works the other way. People don't bring hand luggage because they plan based on the cheap fare only to discover it doesn't include that.

The only reason prices are advertised as such is that they can initially stand out as being cheap. Many people will just go for it because it's hard to make an apples to apples comparison with an airline that gives you everything in a single package. Services that are now in a race to the bottom (airlines, mobile operators, etc.) are using these strategies more and more to differentiate themselves. But it's all done through misleading advertisement.