I'm stuck finding a word to use for somebody who thinks he has tech skills because he can use the latest trendy mobile apps, though in fact he knows nothing about technology (e.g. how an app is made: how to create it).
A person who knows how to use a fancy state-of-the-art app with great ease and familiarity is just a competent "user", they are not a developer or programmer.
A user (computing) is a person who uses a computer or network service. Users generally use a system or a software product without the technical expertise required to fully understand it. (Wikipedia)
I might refer to this person as a "non-nerd" but I admit I don't know if this was a commonly-used expression, it makes sense though.
If the person's skills with the apps that they use are significantly above average, I would described the person as a power user of those apps.