The article seems to have been written by someone who has a poor grasp on security terms.
I'd recommend reading the researcher's write-up and avoid getting the wrong idea of what's happening there: https://www.avoid-coinomi.com/
It frustrates me that unfamiliar people are going to see this article (or ones about random fly-by-night exchanges running away with deposits) and just come away thinking this type of problem is an unavoidable part of cryptocurrency, which it's not. Maybe it is for people who don't do their research, but I'm not telling them to use cryptocurrency. I hate that whenever there's talk about cryptocurrency, these amateur cases dominate the conversation. It'd be like if every time the act of camping was brought up, people were aghast and talked about how unsafe camping is and how it's a horrible thing because of how some family died camping recently (after they went camping in the middle of the desert without supplies).
It seems rather likely to me that something like this would never be spotted by looking at the source, you'd have to analyze the application at runtime.