While I'm studying(or doing anything in my life), my brain wanders around(daydreams, stresses, remembers unpleasant memories and thinks negatively about the future) so I notice that and then bring it back to focus again in studying. Isn't that the same thing as mindfulness meditation? in both things, we focus on or attend to something and when the brain wanders around, we bring it back.
I read articles before 1 2 that say the difference is that in mindfulness, you let things(that you attended to) go after you finish without thinking about it again.
Does that mean that I can call studying a mindfulness meditation if I stopped thinking about it after finishing?
It is question I've been asking myself as well in my experience with mindfulness meditation.
Meditation is not manipulating experience, it is simple noticing it. Furthermore it focuses on sensory experience which seems to be inversely correlated with our narrative experience(Farb et al., 2007).
Being focused on studying involves planning and invariably it adds a narrative feature to our experience. Mindfulness increase grey matter in areas associated with executive control(Hölzel et al., 2011), hence we can hypothesize mindfulness is good for more effective studying.
There might some type of false placebo effect in studies reporting increased focus due to meditation.
Farb, N. A. S., Segal, Z. V., Mayberg, H., Bean, J., McKeon, D., Fatima, Z., & Anderson, A. K. (2007). Attending to the present: Mindfulness meditation reveals distinct neural modes of self-reference. Social Cognitive and Affective Neuroscience, 2(4), 313–322. https://doi.org/10.1093/scan/nsm030
Hölzel, B. K., Carmody, J., Vangel, M., Congleton, C., Yerramsetti, S. M., Gard, T., & Lazar, S. W. (2011). Mindfulness practice leads to increases in regional brain gray matter density. Psychiatry Research, 191(1), 36–43. https://doi.org/10.1016/j.pscychresns.2010.08.006
First, mindfulness meditation is a practice that involves attention regulation and adopting a particular orientation toward one's experiences in the present moment . Your example has largely described the first component—paying attention to the current moment. The second component has been described as relating to one's experience within an orientation of curiosity, experiential openness, and acceptance. The consequences of this component include cultivating a non-reactive and non-judgmental attitude .
Second, there are formal mindfulness practices like mindfulness-based stress reduction (MBSR) program , and "informal" mindfulness practices namely mindfulness of everyday activities (e.g., mindful eating, mindful walking), mindful reading, in your case.
In short, mindfulness meditation cultivates focused attention, and focused attention is part of the practices involved in mindfulness meditation.
 Bishop, S. R., Lau, M., Shapiro, S., Carlson, L., Anderson, N. D., Carmody, J., ... & Devins, G. (2004). Mindfulness: A proposed operational definition. Clinical psychology: Science and practice, 11(3), 230-241.
 Baer, R. A., Smith, G. T., Hopkins, J., Krietemeyer, J., & Toney, L. (2006). Using self-report assessment methods to explore facets of mindfulness. Assessment, 13(1), 27-45.
 Kabat-Zinn, J. (1990). Full catastrophe living: using the wisdom of your body and mind to face stress, pain and illness. New York: Delacorte.