Most conflict is asymmetrical. Many times the 'source' of the conflict has no idea that their actions are perceived negatively by others.
As an example, it someone (as a biker or runner) surprises/startles a walker when they pass the walker, the biker/runner may have no clue that their action was perceived as a negative.
Also conflict can be real or perceived. Normally conflict is only perceived, and it rarely escalates to gestures, words or physical contact.
Either way its still conflict.
As a runner (or biker) almost everyone can remember a time when they perceived conflict. (Example: being startled and or scared by a car as they gun their engine or pass too closely). Most of the time the person experiencing the conflict never gives an indication that they were upset by something.
Not condoning the runner's actions in this case, but at least he warned the biker that he experienced conflict before it escalated.