Imagine this: you're walking down the road and see that far off, 3-4 tiles away, there's a guard standing in the swamp. Running after it would take at least half a day.
And it's clear that the second or third guard was probably standing on the road, and the opponent broke through them. But it's not 100%, who knows what the map generator will do.
That's why, in questionable situations, it's suggested to ask the opponent.
P.S. I'm fundamentally against using tech units in situations where you can do without them. This situation falls into that category.
The opponent is not obligated to tell you anything!
If you're looking for the truth, observe the passage. When the opponent passes by the guard, it means they broke through it. Or, increase your dark vision skill to expert :)
Why should I tell you something that doesn't concern the opponent???
I didn't influence his moves by breaking through or not breaking through this guard; if you want 100% certainty, break through the passage yourself!!!