Why Does Lyn's Mode Have Ambush Reinforcements?

Lyn's Mode (Normal) doesn't ever teach the player about ambush spawns (or ambush reinforcements, or same-turn reinforcements) or that they're likely to come from Forts. Weird thing to put in the tutorial when the main game tends to exclude these.
Footage from Chapter 8 of Fire Emblem 2003 (GBA); or Fire Emblem: The Blazing Blade.

[@PrinceOfKoopas]

Kishuna is a same-turn deinforcement.

[@krissjames7276]

I appreciate Fire Emblem Engage posing a decent challenge without relying on that kind of bullshit.