John Gill Commentary 2 Samuel 18:26

"And the watchman saw another man running; and the watchman called unto the porter, and said, Behold, [another] man running alone. And the king said, He also bringeth tidings." — 2 Samuel 18:26 (ASV)

And the watchman saw another man running
At a further distance:

and the watchman called unto the porter ;
that kept the gate, under which the watchtower was:

and said, behold, [another] man runneth alone ;
as the other, and has the same appearance of a messenger:

and the king said, he also bringeth tidings ;
it being usual then, as now, to dispatch one messenger after another, as fresh accounts coming in made it necessary.