Ambushes in the turn they are placed

We had a question arise in a gamer tonight.

Player A attempts to move his FL into a wood, revealing an ambush therein. The FL stops short of the revealed units.

Player A then attempts to move another unit from the same command into contact with the just placed ambushing units.

The ambushing player claimed this was not allowed - that ambushing units could not be attacked in the turn they were placed.

The counter argument was that only the unit revealing the ambush could not attack.

Who was correct?

I suppose you are using the rules of Advanced.

Player A move his first (exploring) Unit. Mind that B must reveal his Unit after the movement of A is completed. So could be wise not move too close to avoid surprises.

After the movement of A, B puts his Unit(s) on the table, he can place where he wants provide they are inside (for more details see Advanced) the terrain feature. Doing so B can place his Unit in a way to deal with other possible incoming enemy. And of course another Unit of A can charge him.

Making ambush can be risky as a Unit can found himself isolated.