A variant of this message comes up before every Besieged when the approaching army moves from "Preparing" to "Advancing" status. But... does it mean anything?

I have a few times gone out into the areas bordering Al Zahbi and waited for the beastmen forces. I see them coming, but they ignore me. They don't aggro, and they don't even slow down if I take offensive action. It seems like the warning to "intercept the enemy forces" is just flavor text. Unless... is there something I am missing?