How did Daredevil know the journalist will throw a cigarette?

Now first of all, as already pointed out in the other answers and in the comments, this scene is far from plausible. Above the matter of knowing where people throw their cigarettes, you also have considerations of the fuel staying in place, noone else noticing the pool of fuel lying around, or Daredevil taking the time to construct it. This scene is simply played for effect and you have to accept that it might not be backed entirely plausibly.

However, you might notice that the journalist, in his attempt to convince the detective (or call him out on his dishonesty) that it is indeed the infamous Daredevil who is behind this, deliberately throws his cigarette into the fuel in order to light it. This suggests, that it is actually Daredevil's modus operandi to leave such burning marks and the journalist is very well aware of that. This explains why the journalist knew to throw his cigarette down (if we ignore that he also knew exactly where) and it might as well explain how Daredevil knew that he was going to do that: you can say he leaves his mark specifically for the "initiated", who know how/where to look for it.