Is this because he saw the second explosion before he heard it? I know sound travels slower than visual.
Sound travels at 1,126 feet per second.
Roughly 600 feet per half second. Do you think you could react and say “Here it comes” in a half second?
And, in all likely hood he was much closer than 600 feet, so it would be less than a half second to react and say “Here it comes”.
Doesn’t seem plausible that you would see it and make a statement in that amount of time unless you were a good distance away.