Tesham Mutna Sword does not trigger Onslaught

Hi fellow Gwent players

I recently started to play an Onslaught Deck with Tesham Mutna Sword, and discovered something I am not sure whether it is intended or not.

Ability of Tesham Mutna Sword:

Damage an enemy unit by 5.
Repeat once for each status it has.

Ability of Onslaught (relevant part):

[…]
Whenever an enemy unit becomes damaged, give 1 Armor to all Pirates and Ships in your hand.

So my assumption was, that Tesham Mutna will trigger the "give Armor" part, if the unit I attack gets damaged. Even if the sword does destroy it afterwards.

I used it against Ciri:Nova and Donomir of Troy, both cards that the sword is made for.
The attack itself was successful, but Onslaught did not trigger, although the units visibly had a "damaged" status during the attack. Does anyone know whether this is intended or not? Having one armor more or less is not a showkiller for my deck, but it could be decisive in some matches.