The OP case is an example of an act of mindfulness under the third foundation, contemplation of mind or consciousness. The problem is that some modern teachers take the static observer to be mindfulness in total, whereas in some cases that observer must take action, that is why mindfulness is positioned between right effort and right concentration, as it can invoke either depending on the mental states it confronts. In this way it can be seen how the serenity (equanimity) that’s been developed is a tool, as for example in another situation would be the asubha contemplations (right effort). A simile is the person crossing to the further shore on a raft, occasionally the elements may allow them to travel in the right direction by going with the current, but mostly they have to actively work to achieve progress. There was an Australian Buddhist who tried to cross the strait from Darwin to Indonesia on a raft relying mostly on equanimity, and was almost carried past the entire archipelago headed towards the Pacific ocean, fortunately landing on one of the last islands.
"And how is striving fruitful, how is exertion fruitful? There is the case where a monk, when not loaded down, does not load himself down with pain, nor does he reject pleasure that accords with the Dhamma, although he is not fixated on that pleasure. He discerns that ‘When I exert a [physical, verbal, or mental] fabrication against this cause of stress, then from the fabrication of exertion there is dispassion. When I look on with equanimity at that cause of stress, then from the development of equanimity there is dispassion.’ So he exerts a fabrication against the cause of stress where there comes dispassion from the fabrication of exertion, and develops equanimity with regard to the cause of stress where there comes dispassion from the development of equanimity. Thus the stress coming from the cause of stress for which there is dispassion through the fabrication of exertion is exhausted & the stress resulting from the cause of stress for which there is dispassion through the development of equanimity is exhausted.”—-MN 101