Some gain leadership positions by context. While they may not be the appointed leader, given the circumstances and their technical competencies it creates a scenario for them to assume leadership roles.
However these moments could be an acid test for their true mettle as a leader. Those who observe them will watch them closely to evaluate the softer aspect of their leadership style which is so crucial for the longterm assignment of the leadership roles.
Such individuals would do well for themselves if they consciously step out of their obsession on technical competency focus. While technical competency is crucial the leadership in the longer term is really about bringing out the best in others and providing direction, which is much easier said than done.
So if you are assuming a situational leadership role be conscious about the true aspects of leadership as well.