You don't have to have employment, but must have some other means for supporting yourself besides social benefits. It's ok to collect them between jobs for a while, though.
I don't know about you, but I often do side-projects to learn things. It try apply my knowledge into something to understand it.
Maybe you have the same reason and you can say it's for improving or maintaining your competence.
Also, perhaps you shouldn't think too muchs about how to justify things you do to others.