I started out writing a rebuttal to you but the authors don't actually give me much to work with - I can't find a full report, and what I can find, is all about "apps". I think it's pretty likely the actual participants didn't only give feedback on what apps they want, but the study proponents are looking for ways to promote technology, so apps are their interest.

Having said that, there's nothing wrong with doing a pilot study or demonstration study with a small group of volunteers. In fact, when you enrol people in a study and ask them to to do something (as opposed to simply looking at data on what they've already been doing) they're always going to be volunteers - we don't force people to participate in research. So the fact they were volunteers is not a criticism of this study, unless the authors then claimed the findings could be generalized to the whole population (which they don't).