I’m familiar with that concept, but the way those words are presented in the app, it gives the (misleading) impression that that is the way they should be written, when in fact it depends heavily on context. As well, the actual ability of the learner to discern the context matters too.
For example, in Japanese 0, there are many words that could easily be presented in their kanji form, such as だいじょうぶ/大丈夫. But kanji are challenging under even the best of circumstances, so I’m sure they decided to focus on hiragana and katakana for that course.
I get the importance of making sure that students know why it’s important to learn all three (hiragana, katakana, and kanji). Back when I took my first Japanese lessons, while they covered katakana, most of the words were written in hiragana, so it took me a lot longer to learn. And I didn’t understand kanji at all for a long time.
But that being said, it doesn’t make a lot of sense to me to rely on a student’s ability to discern that a word is being used in a particular context and from there to understand that it is being written in a particular way to convey that context. If that’s the intent, there should at least be something to denote it instead of telling on perspicacity.